Over charging customers

I went to fill up my vehicle which was not empty yet before I drive out to Johannesburg. The pump showed a transaction of R200 on the screen before I filled up. After my vehicle has been filled up, the pump showed that my 55 litre tank took 60 litre fuel and my tank was not even empty. I was overcharged with the R200 of the previous transaction. I even called for the supervisor to report it but even the supervisor argued with me that staid g that I must relook at my car's fuel tank capacity. They stole R200 from me for payment of fuel which I did not get.