Given what you were told by the check in desk, I would have assumed it was a free upgrade too. Just thank them, smile graciously and walk away.....

Unfortunately, assumption in this situation is dangerous. Much better to press the person to explain exactly what had been done so you could decide then and there whether to proceed with or cancel the upgrade.

I don't believe that the person didn't know how many miles were required. The system will always tell the operator how many miles you have and how many are required. You should have been told the miles you spent.

Never walk away assuming what was done. Remember the golden rule:
"Assumption is the mother of all f***ups"

Unfortunate for the OP, however there are too many issues here for the story to add up. The OP had apparently forgotten he had a saver fare. He also could have checked online how much an upgrade would have cost. Then he could have queried it at the point of upgrading instead of assuming it was complementary. Then took the seat in F anyway and got upset after enjoying the service.

Also when did you know EK to give away upgrades from Y saver to F for free? For a regular traveller it sounds a bit naive to me.

The other angle to this is there are so many nationalities working at DXB that in my experience you have to be quite explicit. If it was an enquiry from the OP to the agent then better to ask "can you tell me how many miles will it cost to upgrade this sector to F?". I can see how a comment like "can I upgrade to F using miles" might have been misinterpreted by someone trying to be helpful.

Chances of a refund - zero I'm afraid.

OP went from Y to J, not F. One can't upgrade two cabins. One cabin op-up isn't that uncommon, especially for a Play which OP is. But then as Plat he/she should know how everything works and also earn enough miles to get past this

I find the cryptic answer to the question of miles cost to be really odd. OP asked how much it cost. If the employee had given him a straight answer there wouldn't have been an issue here. OP isn't obliged to know how many miles it costs by checking up front and his failure to do so is pretty much irrelevant. The employee should have answered with "yes, an upgrade is possible and will cost X miles, would you like me to proceed?" At the very least they should have answered the "what did this cost?" with a simple "x miles". The answer given makes it sound like OP has been given some sort of deal, or that the employee is being playful in providing some sort of extra.

If I went into a store and, having just handed over my card to pay for my TV, I enquired if they had a service package, I'd be pretty narked if they replied with "done!!!" and when I asked what they'd charged my card they told me "I can't tell you, ho ho ho". I mean really. These miles cost a packet to buy, what kind of answer is "I can't tell you"? Imagine if you'd asked if you asked if they had cash upgrades and they replied with "done" and "I can't tell you".

I tend to agree with OPs read of the situation. My assumption would be that I had a free upgrade, not that for reasons unknown the staff member was refusing to tell me how much I'd been charged for a product I hadn't agreed to buy. So I'd probably also take my seat thinking "Bonus, an op-up".

OP, I'd go ask them to restore the miles. You already have "no" so what do you have to lose?

OP asked if upgrade is available. Only after processed enquired about cost

Understood, but they really should have confirmed if the price was acceptable before processing. But, OK, the agent may have misunderstood the question as a request. Not optimal, but that could happen. But having done so, refusing to tell the OP how much he had paid is just outright odd. I think because it's miles people might be giving the airline more leeway. Although legally there's a grey area on gift cards, miles and other forms of pre-payment, from a customer service point of view that would be a pretty shabby route to take. Seeing things from the customer's point of view (who had just paid cold, hard cash for miles for a specific purpose) there would be little difference between this and the agent charging the credit card to buy the appropriate miles for an upgrade, then refusing to say how much he had charged. I think we would all find that unacceptable, so we should also find it unacceptable that the agent took the assets of the OP without forming the sale contract, and then refused to report what that sale was.

I really think this is one to take further. They might restore some of the miles. My thinking is that OP could argue he WAS prepared to purchase the upgrade if the cost was similar to his usual upgrades. It wouldn't be unreasonable to argue that such a cost would represent value to OP and was the price the OP was prepared to pay.

Really, OP, I would write a polite letter. Don't expect something back, but at very least they might have a word with their staff on protocol (it sounds like this is more than a one-off).

I cannot fathom why the OP would not have done the homework as to what the miles cost might be. To me, that is the logical first step. The OP was certainly aware of the miles needed to purchase the future award flight. Why not this one?

To me, the answer is obvious. The OP was actually wanting an op-up and didn't want any pre-allocated miles involved, but didn't articulate that. The operator's unusual response played into the OP's hope that they HAD just received an op-up. At that point the OP should have sought clarification of how the upgrade was processed, but didn't.

Why would the OP have enquired about a miles upgrade if they didn't intend spending any of the miles purchased for another purpose?

There is fault on both sides here, a lack of clear communication. The OP is not blame-free, and I personally don't think compensation is appropriate.

Who knows? But importantly the agent had no idea either. The agent didn't know whether OP had the first clue about the complexities of miles upgrades. Maybe the flight was a gift, a work-paid flight, maybe OP had no idea how much was paid or whether it was flex plus, etc. Maybe OP had no idea where to look online (which actually seems to be the case). Maybe OP just walked up thinking "Let's ask if it's possible before we start looking at price".

People replying seem to be confusing the question at hand ("was the agent in error giving an upgrade without confirming price and then refusing to inform whether a fee was paid/what price was paid?") with another: "could OP have avoided this outcome?" That second question plays no part in the first as the agent should have ZERO expectations of the OP having done research. As it is the agent executed a transaction unrequested. It is, by definition, an unrequested transaction because one party was not informed of half of the transaction's details. The transaction REQUIRES the agreement of price for goods/service where the seller knows these. The price wasn't agreed, and a) the agent transacted before the buyer could consent and b) then refused to inform the buyer of price. This sort of activity is legally frowned on e.g. when car-repairs are executed without specific agreement on cost. It's not a stretch to say that OP wouldn't find the price reasonable evidenced by two arguments a) previous upgrade costs and b) saving miles for a specific goal.

I think asking how much the transaction cost qualifies as seeking clarification. The agent didn't provide any indication that the transaction cost miles despite being asked explicitly. I guess OP could have asked a second time, but having sought clarification and received an answer that hinted at no cost involved, why should he/she? What if OP did so and got "Shhhh" as a reply? The agent was acting inappropriately, OP has no obligation to compensate for an odd agent by seeking out further clarification. Could have, sure; should have, no. As to hopes for an op-up, I have no idea, that would be guessing.

I think OP's expectation was to make a decision based on cost. OP tried to find out cost, failed using the app, and went to the desk with the intent to enquire firstly if an upgrade was available and then agree to the transaction if and only if the cost was acceptable (i.e. didn't spend the miles he/she was saving for a trip) - that's not unusual. Imagine this happened every time you enquired about availability of something: are there any tickets for the theatre? Done, not going to tell you the cost but you're in the front row. Any seats on this evening's flight? Done, you're on board, how much? Can't tell you that... what do you mean you can't pay the mortgage now?

What actually occurred is OP got an upgrade gratis and had miles taken unauthorised from his account. I think it would be pointless to take that line, but the airline really screwed up here. Let's remember this isn't trinkets. This was an unauthorised transaction for miles that cost $2000. The flippant nature of the agent is poor in this situation. His actual (internal) response to realising that the customer had no idea they'd just unwittingly spent $2000, and perhaps wouldn't have wanted to, should have been "Fuuuuuuck", not a playful smile and a cryptic answer.

Absolutely I agree the agent acted inappropriately and his actions and responses were unacceptable.

My point is that the OP also contributed to the situation. To repeat, considering that he had bought the requisite miles for a future award flight and had already purchased the maximum miles possible, why on earth would he risk his miles by asking if a miles upgrade was possible?

The OP is platinum, he has been around the traps for a while and no doubt has a grasp of how upgrades work, despite his not thinking to look up the miles required. So again, I believe all this points to him approaching the agent wanting an op-up, and he enquired in the usual way people do when hoping for one.

The agent's response was unprofessional and unacceptable and worthy of reprimand. I agree with all the points you make in your tome.

But it takes two to tango. My point was that BOTH parties are at fault.

Any updates on this situation OP ?
Was any compensation seeked or offered ?