Happened to me, and I did some research. Support for this problem in COD4 ended a few months ago. I think this list exhausts your options now:
1. Find a modder and convince them to reset your COD4 stats. Dangerous. I tried this and was not satisfied, as certain perks were locked out.
3. Deal with the damage. I love COD4 too much to settle for this.
2. Change your gamertag and create a new account with your old gamertag, starting anew. I was hacked for calling out cheating modders. I will happily level up my profile again just to put it back in a modder's face. As they get reported, they get banned. Filing complaints works. I've recieved emails from Microsoft telling me that I've helped get cheaters banned. I, however, am still playing...