I recently received a bill for repair of damage to a truck I rented that I didn't do. The damage was on the roof of the cab of the truck. When I rented the truck I did an inspection but didn't bother to climb up on the roof to inspect it since I have a bad knee, and I thought the likelihood of damage on the roof was unlikely. Over the weekend I received a bill from National Car Rental stating that I owed $1525.92 for damage done to the cab roof. What is the best way to proceed with them?