Ripping People Off

I hired a vehicle from the AVIS at King Shaka Airport, RA:***, and after receiving my refund of the deposit I see that I was charged an amount of R292.45. Upon taking a closer look at the invoice I see that this was for petrol. I called the branch and they confirmed that this was for petrol. I said that this was strange since I filled the vehicles tank before dropping off the vehicle at the garage situated less than 1KM away from the drop off zone. I was then told that this is an error on their billing side. Is this how AVIS recoups their \cheap"rental charges from customers"