Charged for more petrol than my car holds

I went to Caltex Brickfield Road not long after my car petrol light went on, so the car was not super empty. I wasn’t really paying attention when they filled my tank although I was a bit surprised they steered me to a pump on the opposite side from my tank. I was shocked to find it cost me R100 more than usual – R733 when I usually pay just over R600 for a full tank. I asked them if petrol had gone up and the guy seemed to hardly understand me. I asked again and he muttered it’s always going up. When I got home and looked at my receipt it said it was for 52.5 litres. My car, a Polo Playa, only takes 45 litres. My husband went back and the forecourt manager, Siya, claimed it was probably due to filling up the air lock. I do not think this would take an extra 7 litres, and my car was not actually that empty. Plus every time I take petrol they fill it up as full as they can and it never comes to this amount. So I went back the next day when the manager was there, Vishen (sp?). He was completely unhelpful. He just kept saying his pumps were calibrated and he could prove this. This was not the point, I am not disputing that the pump dispensed 52.5 litres, but it clearly could not have all gone into my car. He claimed the pumps automatically go back to zero after dispensing so I could not have been charged for someone else’s petrol and said he trusted his staff. It seems obvious to me that some of my petrol went to someone else as my car does not even hold that amount of petrol! Had he agreed to refund me the additional amount out of goodwill I would probably have just forgotten about it but now I am being left feeling done over.