Hertz at King Shaka ripping me off for Fuel Charges after returning Car with FULL TANK

Hertz Car Rental at Durban Airport charged me again for Fuel, although I returned the Car with FULL FULL TAN**** Same Story last Year at Durban Airport as well! The Story: Before dropping the Car at Hertz at King Shaka Airport, which is just approx. 200m away, I filled up the Tank on FULL FULL, and now they charge me for a 1/8 Tank = R215.00 to Fill Up at their Depot, equivalent to approx. 15 Liters of Petrol. Either, that is common Praxis at Hertz, or, someone is filling up their own Car, and charging us for it, or, syphoning Petrol out of the Tank for their own Use!! This is totally unacceptable and should be investigated! After contacting Management at DUR Airport Branch, there is NOTHING Customer Friendly coming from them, eg. the Manageress LENUSHA hardly responds! I will NEVER AGAIN hire from Hertz!