Payflex PAY BACK THE MONEY that is mine!!

Payflex PLEASE pay back my money that your' system made me overpay by a full R400 installment which is still not refunded back to me!!...I emailed you on the 26th of July already, ticket query 969945, and then I emailed again on the 31st of July since I didnt get any response, but till today, have not been contacted by anyone of your company, eventhough its claimed a 72hrs response time.