Well, I logged a ticket about this and got a speedy reply. Apparently they think the cards are still on my character, and requested a load of information that I won't be able to supply. (Time I logged in and noticed they were gone, channel of that, time/channel I received them, etc.) Now, that sounds like info they would need to look things up in their transaction logs, so I'll do my best, but who the heck remembers things like that?
I may be able to give them the time I received the cards, because I tried to screenshot that, but if (as usual) the SS didn't work, I'll have to be vague about that, too.
Oh well... at least we can make them aware of the problem. They probably copy-and-pasted the code from the Thanksgiving free tickets, without remembering that they also vanished.