Over Charge

We have put petrol in at Engen Bluewaterbay for the past 1 and a half. Every time you ask for an amount they go over that amount by 5 cents or 7 cents. When query it the petrol attended says that that keypad isn't working. This has been now more then a year. The owner says now that he has been happy with out the keypad for 23 years now. He says that they only operate the machines the problem with the pumps is engens problem and that engen is the one that deactivated the keypad. The owner is arrogant says that if we asked for 400 and they put in 400.05 we need to pay it as we received it or they need to suck it out so now if they suck it out how can I be sure that they don't take more then 0. 5. Every time they go over I fall in a different bracket at the bank and get charged more. This is unacceptable.