To avoid such problem, I always walk around the car upon rental and check if there is any dent or scatches and inform the rep on site. In addition, I take pictures of the car, any dent or scratches I can find. My last rental car had lotsa scratches and upon return, the rep notices them and I informed him there and then that I have pictures to show that those were there when I picked up the car. That was noted on the receipt and I did not get any issue with the rental company.

Please keep us posted if your issue gets resolved with the rental company.