Problems with a local mechanic

Two months ago I was pulled over by the Police in Worcester MA. They told me that I was driving an unregestered uninsured car. In december I changed insurance companies and decided to mail in the paperwork to the RMV instead of going to a local branch. I didn't think anything of it as I had copies of the paperwork I mailed in in my glove compartment. Anyways the officer towed my car and I did the necessary steps to fix the issue with the RMV. Since my car needed repairs I contacted the company that towed my car and signed a paper for the $1200 in costs for the repair work. I did not hear from them for three weeks as I was in the hospital and when I got out I called and asked what was going on with my car they told me I owed them $1800 as they where charging me additional storage fees for them having stored my car for two weeks. They never contacted me to tell me the car was finished as I checked my voicemail twice a day while I was in the hospital and would have had someone pick up the vehicle if they told me it was done and that their would be additional storage fees if I did not get my car. They now have threatened to auction my car as they say I owe them $3600. I am on disability and do have an auto loan on the vehicle. Is there any actions I can take to stop these people from auctioning my car off? They keep increasing the amount I owe and I do not know what to do. I will pay the $1200 I agreed to but that amount is even frustraighting as the towing and costs incurred by the police action should never have occured as I showed the officer the documents that I mailed into the RMV. Here in Mass the registry actually charges additional fees if you go into the branch office instead of mailing the paperwork to them.