Overcharged at pump

It happened on the 14th November just before 6am. The attendant told me to go pay inside because it was before 6 and he didn't have the machine yet, which I did. When they gave me the slip I saw that the amount was over R600 and I couldn't believe my eyes as I've had my car since 2006 and had NEVER paid that much. That's when I noticed that the litres were 51.05. I told them it's impossible because my tank capacity is only 35 litres. I asked to speak to the manager and Jack came to me and said he would let the owner know and that he would contact me. I can't remember his name. I then went to gym and from there my husband and myself went back to the garage but the owner had still not arrived. Jack said he would phone me. I then went to work and the owner eventually phoned me at about 11 to say that he was going to do an investigation but that he would not reimburse me. He said it's possible for my car to take 50 litres if it's empty. I told him that I have owned my car since 2006 and always drive it till the light comes on (about 450km's) and it had never taken more that 35 litre. Gateway Chev confirmed that it can't hold more either. This man must get exposed.