Hertz Fuel & Refueling Charge

When I returned my hire car to Durban King Shaka airport the Hertz offices were not open. Prior to returning the vehicle I filled it with fuel at Sasol King Shaka, which is a couple of hundred metres from where I left the vehicle (next to the Hertz hut).

I was honestly astounded to be charged for fuel R52 and a refueling charge R25.

It would not be possible to put R52 of fuel (+-3 litres) into the vehicle when the vehicle tank was full.

I wonder if Hertz charges everyone returning vehicles outside of office opening hours a fuel and fuel charges as a standard, whether or not the vehicle has a full fuel tank? This appears to me be at best a **** and at worst *****.