Charged for vehicle previously damaged

On the 5th of August, we collected our hire-car from Avis Cape Town International Airport. We walked around the vehicle with the Avis inspector and pointed out all of the marks, dents, and scratches that we saw on the vehicle. There was a particular, perfectly round dent that we pointed out on the side of the car that the inspector told us not to worry about. We returned the vehicle on the 11th of August. On the 12th of August I got a phone call to say that there was a mark on the vehicle that was not on the inspector's report and that we will be liable for the repair costs. I was sent an email by Avis with one photograph of the dent and one of the front of the vehicle to display the number plate. We double checked our copy of the report and low and behold that mark was not noted, when we, pointed it out on the day. We contacted Avis and tried to explain that the mark had been there when we collected the car and that their inspector, who was eating a lunchbar with his other hand, while doing our paperwork, told us not to worry about it. We have just been charged R4400.00. for damages. This was the second time that we have used Avis Cape Town International and it will be the last time. One of their staff member's negligence has cost us R4400.00. Disappointing and unprofessional to say the least. Make sure that you check the inspectors report against what you have seen and take photo's of every single mark on that vehicle before you leave their parking lot. When you drop the car off, make sure that you are present while they inspect it again, especially before they move the vehicle to its final parking bay. Do not be as trusting as we were.