MFC Nedback

I have been a client for the past 4years and my debit order takes place on the 27th of every month for the past 4years and I have never missed a payment but to my surprise MFC Nedbank has debited my account on the 24th of Jan and Feb. In January luckily I had money but now in Feb I didn't have money on my account on the 24th so now my bank personalized me R56.60 for the Bounced Debit Fee. I would like to know how do you change someones debit date without contacting them like you always do when you sell your products? This is unacceptable and a bridge of our contract.