What can I do if the garage shop is asking me to pay for car nicks and dents that was already there when they loaned it to me?

I live in a no-fault state. My personal vehicle was damaged and I picked a local collision shop to fix it who advertised that they would either cover your deductible or give you a free loaner car while fixed. I went there, the owner insisted that I would never be able to get my deductible waived, even though my car was hit while parked and unoccupied. He tried to get me to agree to me paying them part of my deductible and they would pay for "a few days" of the "free" loaner, stating it would only take a week at most to repair my car. I was able to get the deductible waived, so there was no paying them money for that, so I got the loaner car. When I got their loaner, even though a newer car, it still had a lot of dings and missed spots in the paint. They refused to mark any of this down stating they knew where all the damage on this particular car was at. When I returned the loaner, first they wanted me to pay a week of charges for it, out of the 2 weeks they had my car for the repair. Then on top of that, they said there were new nicks in the paint that I must have caused. These con-artists refused to remove my now repaired vehicle from their locked and fenced lot until I made an insurance claim for the damage with my carrier, Geico. So I did this, on the phone, even though they said it could most likely be buffed out. A month goes by, I get a call from a Geico adjuster, he tells me that he has not been able to look at or do an estimate on the rental car because each time he goes to look at the vehicle, it is rented out! So an adjuster never saw the car, they rented it out to other drivers over the course of a month, who could have easily caused a multitude of damage. The adjuster told me that he could not get ahold of the owner or anyone in charge and that when he went in to their shop, other workers looked up the car in their system and said no damage was reported, so basically I made the claim for nothing.