The no international stickers policy strikes me as odd -- AZ stickered LOTS of international tickets with the LCA deal (mine being one) and I don't recall ever seeing anything about stickers being invalid or anyone having any discussions about stickers and some of those tix involved carriers other than AZ (in addition to Cyprus Air, that is). AC may have that policy, but the OP says AZ also didn't like its own stickers. Odd.

Credit card charge dispute seems a good alternative. Good luck!