Engen Jean ave centurion

I put petrol in the other day and they charge me twice for the same transaction. now when u bring it to management attention they argue with me that the transaction only when thru once. They are stEaling money from innocent clients. I swipped my card the first time and it didn't go thru and the cashier said it declined and I should swipe again but I got TWO sms on my fone showing the notification has gone thru and I never got a sms stating the transaction was reversed. THIS ALL HAPPENED AT ENGEN GARAGE ON JEAN AVE CENTURION. It has been nearly a week now and I'm still waiting for management to get back to me. when I contact management about it they just tell me it only went thru once