Car sold privately, now car is allegedly total damage

Hello, I sold my car about 2 months ago, 13 years 180000 Km. I mentioned all the damages and defects that were known to me and kept the “worst” in the purchase contract. Buyer was even three there, everything looked at it. Then I was asked after a test drive. The buyer asked me then also if I would agree to drive to a workshop (even workshop of the car brand) which the buyer had organized in advance by telephone. No problem. The buyer asked if you would come by car through the Tüv, which would have expired a little later. The mechanic said yes, that should not be a problem. We are then back again and the buyer wanted to take the car with you immediately. Since Tüv was standing and we unfortunately had demolished the mirror the day before, I even came to the buyer in price still. Already on the to the home Then a few days later a light should have been turned on. Then the seller complained a few days later that the car had not started in the cold. And now, 2 months later THE call. Buyer would have been in the workshop with the car because of Tüv etc. and then one would have found that the car had to be repaired for about 2500.- so that it would come through the Tüv. They then assumed to me immediately fraud. I was completely perp lex. I had communicated everything that was ever done on the car, had even in the “talk” it was more a discussion on another side, still offered to send all invoices to him, so that he had all this again in writing. But it was still discussed. It was too colorful for me at some point and I asked again and again what to expect from me. But I could also have told everything, that was not for the buyer. I’m just a layman, I don’t know like a mechanic. n times what was broken I went to the workshop because I had no idea. The buyer now said I should take part in the repair or take the car back (the accompanying person who was with me). But do I know what was done with the car in the last few months? I then said to the buyer, if he thinks he has been cheated, then he should go to the lawyer. Or could I have reacted in a different way and how can I proceed now? Did I sell the car with the best conscience? T and everything I knew was also my first car sale. I’m really frustrated.