They would have carried out a vehicle health check when you dropped it ofvthat you would have signed, so if the damage isn't shown in thefe then they have noeg to stand on!
I had damage done to one of my wheels and passaner door when I droppes mind off for a service. After a month or so of constant forward and back, me chasing them up, I finally got a cheque off them to cover the costs. They had offered a 'good will' gesture and fix if themself, I literally laughed at them and said my car is never going near them again, I want the money. Took a while, but I got there in the end :)
Best of luck!