Feeling very frustrated and wondering if anyone can suggest anything, other than just enjoying what I've got.

Availability for FRA-DXB in F came up about a week ago for my flight in October. Great, I thought, phoned the ICC to confirm I would like to change to F and was told all ok. Cash taken, then phone call saying that they couldn't ticket the changes (although I had already logged into My Booking and chosen seats etc) as the booking was miles+cash. Fair enought I thought, annoying but it's what I had been told above anyway. I checked how many miles I would need and started transferring them from AMEX. Most went through ok, but then one transaction didn't and, according to AMEX, the transfer was refused by the partner i.e. BMI (turns out you can only due 1 transaction per day).

Anyway, it took a week longer than it should have done due to the bank holidays, but today the miles were in my account. I phoned ICC and was told the flight was available in F but it couldn't count as a change (from miles+cash to miles only) and I would have to cancel and rebook. I explained that I didn't want to have no seats so said I would make the new booking and then cancel. At this point I realised I didn't have enough miles and ICC can't hold seats so decided to cancel the flight presuming seats would still be available when the miles were credited back to my account.

Luckily, before cancelling, I asked the agent to check availability for the flight and was told there was no F or C availability for the flight. Now, one agent said I could use a voucher to upgrade, but I was wondering what voucher this would be (to maybe trade in Coupon Connection) and whether the agent was correct? This is likely to be my only chance to try the F terminal in Frankfurt, and so I want to do what I can (also I mentionned to my wife that F was available and I would get the seats as it's her birthday so don't want to be in the dog house!).

So my question: what voucher would enable me to upgrade the flight without cancelling it first? If there isn't one, would I be able to pay upgrade at LHR for the FRA-DXB leg, and is it reduced or just the difference in fare?

Thanks

Price123