Towing Issues: Sold a car, it was towed, other party never registered., dmv california, collections agency

Question
I sold a car before July 4, 2006. The guy I sold it to never sent in his part of registration. I sent in my release of liability through the mail to Sacramento. July 4 was a Monday (a holiday) and the police came to my house saying someone stole my car and stripped it. I said to the cop it was sold this weekend and I no longer own it. I gave them the information of the party who bought it and they left.
Just now in October, a collections agency on behalf of the towing company who towed the car are asking for $2000.00. I already requested the release of liability from DMV California, but the Collections agent told me something about it being stamped before the date of sale. I checked with DMV, and they assured me I'm okay and that they recorded my release of liability on July 13, 2006. 9 days after the car was towed. Am I alright if I show the towing company that I had release the liability of the car before July 4th (the day the car was towed)? Or do I need to get a lawyer? The guy I sold the car too never answers my call, and I don't know if the police or court system helps out in this.
Any direction is much appreciated.
Thanks

Answer
Did you have the Buyer sign a Bill of Sale stating the make, model and year of the car and perhaps the VIN and THE DATE you sold it to him, with his signature. If not you should have. People sell cars and buyers never register them. They just continue to drive them with the old plates and registration trying to save money.If you had auto insurance I suggest you tell your story to your insurance company. If the collection agency comes after you, which I doubt, your defense is your DATED bill of sale. Generally towing and storage companies just keep the vehicle for their fees and charges, selling off the parts or the whole car.