BEWARE !! Avis overcharging for fuel

I comp**** with the world wide to return a rental car with a full tank of petrol to George Airport in South Africa. I made a point of pointing this out to the person accepting the car on return and took a picture of the fuel gauge and kilometers done because I was charged for fuel on a previous occasion when I returned a car with a full tank of fuel to this airport. I received my rental receipt a few days later and again I was charged for 9 liters of fuel which would have meant the person had to drive the 16 kilometers back to George Cbd to refuel an already full fuel tank and then charged me for it. Avis refuses to refund me for the fuel when I complained.