Still charged for fuel even though I filled up the car before dropping it off.

I rented a T-Cross at the Port Elizabeth Airport recently. When you collect the car you take them at their word that the fuel tank is full, plus you see the gauge at full tank. I dropped off the car in East London Airport 5 days later. I filled up the fuel twice, the last time at the Engen station opposite the airport 30 minutes before I dropped off the car. The lady inspecting the car asked if I filled up and I told her that I did. She then asked for the filling station receipts. I told her nobody told me that I must bring receipts to show that I filled up. Hertz still charged me R274 for fuel plus R25 for taking the car to the filling station. When I enquired about this charged they sent me receipts showing that they filled up and they said I did not fill up the car correctly. Since I did not have receipts to show that I filled up they refused to reverse the charge. I NEVER had this experience with other rentals like AVIS. I always fill up before dropping off the cars and I NEVER had people telling me that I didn't fill up the car correctly. NEVER AGAIN will I use Hertz. Will stick to AVIS.