Early Debit

I normally browse through my Bank Statements on a monthly basis, and I scrutinize them every 3 months, upon scrutinizing my Bank Statement, I noticed that MiWay debited my account early for the month of September 2015 (the agreed debit date is the 20th of each month), and at that time i didnt have sufficient funds on my account, but the bank honoured that payment to MiWay, thereafter they charged me the Honouring Fee of R90, who mandated MiWay to debit me earlier for that particular month? This is totally a breach of Contract from your side, I demand that you credit the honouring fee that was charged by the bank into my Bank account ASAP.