Thank U card - not working. = NO THANKS

Thank you card - not working. = NO THANKS.

I have an Edcon "Thank you card" which I have been faithfully swiping at Engen Garages each time I put petrol in. I have done this for over a year, and I assumed there would be an useful amount of credits on this loyalty card. When I tried to use the card at the shop, I was told that the card "doesnt work", yet when I buy petrol, I get the message on the receipt saying that the card was successfully swiped. Anyway, I have tried the call centre, and emailled the help desk many times, and this has been going on now for many weeks, and they seem to be unable or unwilling to sort this out.