Woodford car rental after sales

The sales employees are helpful in every manor. The after sales though is a different story. I returned the vehicle just under full not even a 1/16 of a tank used, I am then charged for a full tank of fuel. When I query it I get responses that don't make sense. Then I called the call center, they Lodge a "investigation" and say they'll keep you updated. A day goes by and no update. So I call again and get the same results "we will call you before the end of the business day sir". I still haven't gotten a call or mail. I don't mind paying for the fuel used. However I filled the vehicle with R895.50 which was about 42 liters. They want to charge me R1411.80 for full tank. This I believe is in ********* and unfair.