What can I do to prove a fine was paid? CA?

I agree with Julie N. Court fines are not paid through the DMV. They are two separate entities. If you paid a significant amount of money at the DMV, it was more than likely for registration/late fees. In addition to asking the DMV for a complete record of your payments, I'd ask the Court for a complete copy of your "file." (It's usually just the ticket attached to an envelope where correspondence/receipts are kept. If it turns out that you paid the DMV the right amount of money, you still owe the Court and unfortunately, you're going to owe them even more due to the mix up. Good luck.