Charged Old prices for fuel.

I went to engen FW MOTORS in upington today as I was suspecting that they still charging motorists on the old fuel price, I inquired from the attendant who assured me that they prices are updated, The overhead board and pumps reflect the correct prices but we're being charged on the old price and this was confirmed by the cash slip I requested, is this even ethical business behavior. Are we going to be refunded for the extra charge? Who regulates these companies. Who is responsible to make sure that legislation is being app**** accordingly