If you have found out you were a victim over four years ago, did you find out by pulling your credit report or through notification by an entity. Either way, the statute of limitations civilly may not have even begun since you just discovered it. If you just discovered it and it was through no negligence of yours, and you know who did it, you may have time to sue for reimbursement and of course, for any statutory damages that are allowed by California and perhaps even federal law. As to criminal violations, there may even be a way to file criminal charges and depending on the extent of the theft, different law enforcement authorities may be involved.