Complaint sub-issue: Account information incorrect

I purchased a vehicle ( XXXX XXXX XXXX ) from XXXX XXXX XXXX on XX/XX/XXXX, and the vehicle was under a 30 day or 1000 mile warranty. I brought the vehicle back during this time because it was having shifting issues and shifting hard. The auto dealer said they would take care of it and put me in a loner vehicle. The loaner vehicle was absolutely filthy with old food, trash, and cigarettes all over the XXXX. The dealer called a few days later and stated that my vehicle was repaired, but nobody there could tell me what had been done or even where they had taken the car for repairs. A few weeks later the car started doing the same thing again, but the warranty had already expired. I took the car to my mechanic several times over the next year that I had the vehicle. In XX/XX/XXXX I put the vehicle in the shop again and spent {$480.00} on repairs but was told that it would not fix the issue and that they recommended that I sell the vehicle and buy another vehicle. I contacted XXXX XXXX XXXX  again on XX/XX/XXXX and told them all of the problems that I was having and all the money that I had spent. The lady I talked to on the phone told me that I could bring the car back and that they would fix it and resale the vehicle. I asked the lady if it would hurt my credit and she said that it would show as a voluntary surrender but that I would not owe them anything. The lady told me that the approximate {$5100.00} that I had paid on the vehicle and the vehicle itself would cover the purchase price of {$12000.00}. I returned the vehicle to the dealer clean and in the same shape that I purchased the vehicle in ( only put about 16000 miles on the vehicle ). I started the process of refinancing my home in XX/XX/XXXX and discovered that the dealer has put on my credit report not only that it was a voluntary repossession but that I owe them a balance of {$6200.00} and that I was late on 4 months payments. I was never late on payments as they were taken directly from my bank account. After I returned the vehicle I did place a stop payment on the company because they took an additional payment after I had spoken to the lady and returned the vehicle. Since XX/XX/XXXX I have written 3 letters ( XX/XX/XXXX, XX/XX/XXXX, and XX/XX/XXXX ) asking for an explanation of this debt, sent the letter via email ( XX/XX/XXXX, and XX/XX/XXXX ),  disputed the account with XXXX, and filed a complaint with the XXXX XXXX ( XX/XX/XXXX ). XXXX XXXX XXXX has yet to send me a single bit of proof that I owe them anything, and is refusing to remove this from my credit report. I do not dispute that there should be a voluntary surrender of the vehicle on my credit report, but there should not be any late payments reported and there should not be a balance reported. I have attempted to resolve this issue with the company but they are combative and refuse to provide any proof of the debt. I need this resolved so that I can move forward on the refinance of my home. I am a single mother of 4 wonderful children, and work 3 jobs. I have spent countless hours working on resolving this issue and XXXX XXXX XXXX just keeps refusing to provide any information. I am also sending a certified letter to XXXX XXXX XXXX today XX/XX/XXXX stating that they have failed to provide proof within the required 30 days and are supposed to remove the disputed information. If I can not get this resolved I will be forced to get my lawyer involved and possibly sue.