I got an e-mail from Cryptic last night that they resolved the Black Friday charge rewards issue. They did what I suspected would be the easiest way of dealing with the matter, which was to give everyone affected free extra "reward points" so that they'd be able to actually buy all the rewards they had been promised (shock, horror).
In fact, I suddenly had enough points to hit "claim" on the owlbear a second time! Not that this actually resulted in a second owlbear in game, but I figured it couldn't hurt to try. I can't really complain about not getting a second owlbear as that certainly wasn't what had been promised.
I am mollified for now, but I'll certainly approach any future promotions like this with a lot more scepticism.