DL says I was not on a flight that I was definitely on
 

So this is a new one. A flight I took 2.5 weeks ago hadn't posted yet, so I called today and they told me it was because I was a no-show. This was the outbound flight of a round-trip award ticket. The return posted normally. When I look at the receipt online it indeed shows the first segment as "OPEN". The rep called multiple departments who all said I wasn't on the manifest, so I wasn't on the flight, but.....I was on that flight. I just want to get the MQDs for it, but I'm at a loss for what I can do at this point. Curious if anyone has any ideas.

That is why I still print BPs.

I think they would just tell me I printed it but never boarded.

You could try to point out the fact that Delta would've canceled your return ticket had you not boarded the outbound, but per their own records, they have given you credit in acknowledgement of flying the return.

Have them refund you the miles for the outbound.

If you were on a flight but not on a manifest, a GA somewhere is potentially getting fired.

I wouldn't let this go. Someone screwed up big time.

By chance do you have receipts from checked bags?

I had this happen, but it was on the return trip rather than the outbound. The scanner at the airport wasn't working, so the GA handwrote everyone's name and seat number on paper to get us on board. We were delayed about 2 hours so they could submit a manifest manually, and of course my miles never posted (treated as no show). I just submitted a scanned copy of my BP and bag receipts on the website and the credit was there in a few days.

You can check a bag and still no show the flight. The bag is supposed to be removed for international (but not domestic) as there's a security concern that the person could have deliberately missed the flight.

Other indirect evidence that at least helps to establish that OP was at the airport would be a receipt from an airport purchase, a rental car receipt, a receipt for airport transportation (at either end), etc.

If OP entered a SkyClub, DL should have that data.

Oh, good points. I didn't check bags, but I did use the SkyClub and bought wi-fi on the flight, so I can message DL with that info.

Also, this was an international flight (JFK-SXM), so I would have expected some other problem to come up because of this. I guess Saint Martin is just chill about this type of thing, lol?

Likely the agent isn't looking at the reservation. They're looking simply at the ticket, it says OPEN, and concluding you didn't fly. Nowadays miles post based off the ticket. Thus they likely don't know hpw/aren't trained to look at reservations system. I'm betting it shows you onboard. For whatever reason (IRROP, computer hiccup, etc) the flight coupon for that flight segment remained OPEN instead of closing.

if you hadn't boarded, the reservation (not the ticket) would have auto canceled all remaining segments.

Was there IRROP/SDC/SDS/something out of ordinary that happened?

Buying wifi on a flight you never boarded is about as bullet-proof evidence as you can get. Assuming you were traveling alone.

There were no irregularities I'm aware of, and this was the original flight I purchased. But your explanation makes sense, so I submitted a request online with the explanation and wi-fi confirmation number.

Thanks to everyone for the advice...fingers crossed.

Tell them you'd be more than willing to file a complaint with the FAA since the flight manifest was wrong. I doubt this is actually the case though. Can phone agents even see the flight manifest?

Isn't it possible to purchase wifi in advance of a flight? If so, would DL be able to see whether you actually used the wifi on board?