codes have a year before they expire.
What troubles me about your post is that you said you got the maps it promised you but not the skins, yet there is no version of the game you can pre-order to get both maps and skins it's one or the other: survivor edition has skins and hunter has maps, which did you pre-order?
Judging by the fact you got the maps only, it must have been hunter edition.
but if the code actually said skins on it, did you get them off Ebay cos the person who sold you them could have already used them.
Don't forget either that even though games are region free, codes are not so if you have UK xbox live account and purchased US codes they won't work.