Price increase charged before midnight as advertis

A friend of mine who would like to remain anonymous was at the garage to fill petrol before the price went up midnight of the 3rd of june and was charged the increased price instead of the old price,he went back and did receive a refund and the persons responsible stated that it was a system error. I found out about it when the person returned home and was informed and found this bery wrong to over charge a client,the garage claims it was only this one customer and i highly seem to doubt that and i posted the slip on a social forum to inform and create awareness of the situation of what is happening claiming that it is incorrect and wrong to charge the increased price which is only tonstart as from midnight, however the next day an employee meh**** calls me and asks what happend and i explained it to him, later the evening mohammed dangor ( owners son ) calls me and starts swearing at me how can i accuse his dad of being a ***** and i was very calm and tried to explain what happend and that as the result of being charged a increased rate is the reason his dad was called a ***** and mohammed swears and threatened me that i do not know who they are and he will hit and beat me