Double debit on fuel transaction

Went to fill up at the lenchen service station , the engen garage and grabbed some goodies in the shop. Went to pay and they swiped my card, saying system failed did not complete transaction...they swiped it the second time on a different machine... when i checked on my cellphone banking and on my cell it went through twice... i called the manager at the service station... his answer to me is i need to sort this out with fnb... they debited me twice but I need to make sure i get my money back.... what a freakin joke... no sorry or any offering of assitance... very dissapointed and wont be going back to those *******