Intentionally joining servers to exploit is a good way to get laug-hed off the forums. Steam really doesnt care, and their support system is fucked. Treyarch wont care either, and they will probably just laugh you off the forums there.
And even if steam did care, they dont keep backups that could be used for 'fixing' stats, as this could easily be abused. Regardless of what these assholes say, you hacked, and you pay a consequence. Weather or not YOU were the one modifying the game or not is irrelevant.