Unauthorised debit order

My fnb credit card was debited twice. My monthly payment is R393. On the 28th I transfered R500 into my credit for payment which covered more than my monthly installment. Then further on the 31st at around midnight they debit my account with at amount of R393. When I already paid my credit card. That had caused my debit orders which are scheduled for first to bounce as I had just enough to cover my debit order for my vehicle. Leaving me in problems with my payment for my vehicle.