How do I fix this?

Several days ago, I believe over a week, I was playing CoD4 multiplayer. I was a level 20 something. So today I go to play multiplayer again, and to my....surprise....I'm back at level 1. No, no one I played with sent me a message or party invite and I wouldn't remember anyone I played with in matchmaking over a week ago, so assuming this was a hacker's de-ranking for some kind of twisted fun, reporting or anything is kind of out of the question. I just want to know if there is any way to get my previous rank back other than just playing more.