Towing Issues: towed vehicle auctioned off being charged difference in storage fees, storage fees, tow company

Question
Hi, I needed to get rid of a older van that my mom had purchased for me a few years back.  It was run down and I had planned on selling it to the junk yard.  However, I mistakenly let my husband take it to his father-in- law to sell it instead.  That's when things went wrong.  
My father-in-law sold it to someone on a payment plan for a hundred dollars a week.  The person only made two payments and then disappeared.  I immediately wanted to repo the vehicle but my father-in-law wouldn't give us the persons information. Well as expected the van must have broke down and was just abandoned and towed.  Later we discovered that my father-in-law had sold it for more than he claimed and this why he was unwilling to release the bill of sale.
So my mom receives a letter stating she is liable for the storage fees since the van was still in her name!  I call the tow company and explain to them what happened.  That it was sold and suppose to be changed but never was.  The person said then not to worry about it that it would then be auctioned if nobody wants it.
Fast forward six months.  My mother receives a new letter from a collection agency saying she owes $1300.00 in storage fees!  I call again and they say that they only sold the van for $100.00 and that we're liable for the difference.  
Is this right?  I was told that if we allowed them to auction it that we wouldn't have to worry about it anymore.  I live in Texas if that helps any.  

Answer
You will need to get a copy of the bill of sale to prove you sold the vehicle. I hope you took your tags off. It is not your responsibility to make sure that the buyer transfers the vehicle. Once you can prove you no longer owned the vehicle they should not be able to bill you for the balance.