Same here. I haven't even played in almost two weeks and I booted up to download the new maps. No boosting, no cheating, no nothing and I have nothing now. Lost almost three prestige levels. There are other threads on here with the same issue. Sounds like it is related to using the local play and then going to online play.
PM Cutpurse here on the forums. He can help you out. Or, you can go to the Activision Support page on facebook. Or you can tweet Activision support (not sure of the name for them on twitter though) Or you can go to the support section of the fourms and find all your answers there....or you could do all of them. Good luck!!
Remember, there are a lot of players with the same issue so it will not happen overnight.
EDIT : Don't go into system link either. My son did last night and his CaC slots got messed up. I contacted Support via facebook and they told me how to fix it. His level stayed intact but I was able to get it fixed within an hour, so, just keep that in mind also.