Towing Issues: Received tow bill for a car we sold, nv dmv, tow company

Question
Hi.  We recently received a $1000.00+ bill for a car that is being held after being towed this last fall.  We sold this car in a private party sale last summer.  We do not have any contact info for the guy that purchased the car.  We have a bill of sale.  NV DMV does not require a notorized bill of sale, so it was not.  We just called the tow company to let them know it is not our car and they said they would send us to collections.  They plan to auction the car for a few hundred and charge us for the rest of the bill that will continue to calculate at their formula daily.  They said the only way out is a notorized only bill of sale.  The car isn't worth but a few hundred bucks, and it appears it was never registered by the new buyer.  Is it legal to threaten our credit and intimidate us to pay a bill on a car that is no longer ours?

Answer
The laws vary from state to state for collections and what they will allow towing companies to do. If the vehicle is in another state then they have to honor the state regulations where the vehicle was sold. I would contact them, advise them of this and if they do not resolve the matter and a collection agency calls you I would contact an attorney. Did you ever receive any notification that they had this vehicle prior to the bill? How long have they had the vehicle?