Thrifty over charged me for kilometers I already paid for.

I rented a vehicle for two days and paid for two days when I went to pickup the vehicle. I chose the 400km/day so for 2 days I get 800km. I then drove the car for 874km from Johannesburg to Bloemfontein and back. I returned the car a day early but did not receive a refund for the 1 day, which is fine because I used it for 800km. Thrifty charged me 474 km at R1156.94 + VAT which is wrong. I paid for 800km and must only be charged for 74km. I have been struggling since the 10 of Feb to get this resolved with no success.