How to remove a charge off from my credit report?

I had a 2005 Monte Carlo. I paid the car off about three years ago. I assumed everything was ok because when I looked at my credit report a couple months after I paid it off it said paid in full balance zero. I just took a look at my credit report and it is saying the account was charged off and the balance is almost 12,000. I sold the car since then. I don't have receipts of the check I paid them, but I do have papers from them saying that it was paid off, and the original contract saying it was paid off. My question is what do I do from this point??