Miranda, what state was the account originally opened in?
At any time after 2001, did you ever confirm to anyone on the phone or in writing that this is legitimately your debt? Or did you ever make any kind of payment arrangement with anyone after 2001? If you did either of these, it would have restarted the statute of limitations. As someone else said, check the CA trying to get money from you--they may not even be licensed in your state.
The first thing I would most definitely do is send out a validation letter and a cease & desist letter as well, sent certified mail RRR. Due to the age of the debt it is possible that they dont even have the info needed to prove their legal right to collect on it, and if that is the case they are not allowed to take a penny from you.