About 6 months ago I voluntarily gave back my car to the dealership. I informed my creditor what, why and when I was doing this. I received a letter stating that they sold the car and now I owe $15,000.00. They call 15 times a day and have sent many letters. To this point I have not taken their calls. Obviously if I could have afforded the car payments I would have continued making them and obviously I do not have this kind of money to pay them. What should I do?