Not happy with Avis

I took a car at Avis in kokstad on the 29th of October,I returned the vehicle in king shaka airport.the car had a scratch on rear bumper,I was smashed by another car at the robots.it was a hit and run,I was charged again R1760 but I took the full cover insurance with them.to me Avis they are the biggest ****** when in comes to car rental.why did they charge me for a full cover insurance when I had to pay again?