All my sympathy went out the window when you said you tweeted that... Ask for the complaints box/book, by law they must have one, tweeting this wont get you nowhere, nobody cares about a service with a billion-to-1 noise ratio. Even emailing the HQ would be better than twattering that.
Had a similar one, where I've got a copy of Pikmin which has a Australian case but an EU copy of the game (if the part codes are to be believed). Not a major headache, just a 'huh, that's a bit odd' and then continue playing. It might well be the case with some Classics games that they could be rarer than the originals someday (much like with grey-cart Zelda). On the bright side, at least Microsoft don't do what Sony did for the PS1 and PS2 era and have bland, uninteresting CD/DVD labels in comparison to the original. I do wonder whether the print quality is as good on the Xbox/Xbox 360 Classics DVD labels as they were on the originals, as some I've had are quite poorly printed. Can anyone confirm this? (I might post some examples at some point for clarity).