Avis Car Rental Charging For Fuel I Did Not Use

I rented a car from George airport. The car itself and everything leading up to that point was what I would expect from a reputable rental company. However, everything after that was the worst customer service related incident I have ever experienced. Avis charged me for a tank of fuel even though I filled the car up before I handed it back. I have since sent 30+ emails to the customer service team and individuals. I have phoned 8+ times, spoken to the manager, and still no resolve 1 month later, and they blatantly ignore me. I have done the calculations showing them how impossible their claim is that they needed to fill up the tank. I only get half a response when I phone and raise my voice at them. WORST CUSTOMER SERVICE EVER!!! I WILL NEVER RENT A CAR FROM THEM AGAIN.