Frustrated Customer

I'm so irritated. My son went on Saturday to buy gas, the merchant's machine showed declined, after paying twice with my card. He then decided to pay with his own card (Capitec). That means we've paid 3 times for 1 purchase. Only to be told today that FNB is aware of the double payments and the 1 transaction will be reversed. My case is different, I've paid 3 times, therefore 2 transaction should be reversed from my account. I refuse to fill in a dispute form and wait up to 30 days for my money. Can someone please resolve this a.s.a.p. I can provide you with a copy of the payment with his Capitec card.