Storewell crash car - won't accept responsibility

I made use of the Storewell service and collected my car early one Monday morning and had to rush to work. Upon arriving at work I noticed that the car had been reversed into a wall or something of the sort and the back left side of the car was badly damaged. I immediately contacted Storewell but they denied responsibility, the damage was not there when I dropped the car off and I did not have an accident on the way to work so it 100% happened while in their possession. If I had checked the car upon collection it would have been a completely different story.