the issue with the 3 people who were reset in this thread were reset to level 1, but didn't lose calling cards.. This leads me to believe that actually, there was no cheating as such as a ban and reset by treyarch will make you lose everything, however it could have been to an unknown, or known glitch
I wouldn't be surprised however that perhaps there is something that none of the people reset have let us know... The only things I can think of? Is it possible you could be reset, or lose rank because of constantly going over the XP cap? (if you don't know, the amount of XP you can earn per match is capped to stop boosting)
Other questions (which if you're going to reply with assumptions, then please don't bother unless you have concrete proof) - can you get reset for constant violations of being abusive, insulting or breaking other communications Code of Conduct? Can you get reset for having too many emblems reported/removed due to profanity?
Of course it could be a problem with treyarchs servers, so as starbuck says, contact the person he mentions and take it from there.