debit my account before pay date

I have a loan and a credit card with African Bank and my debit order date is for the 20th of every month. If my pay date fall on a weekend I do not get paid early. I don't know who advised African Bank to debit my account a day earlier. This happened 2 months in a row February and March. My bank account looks terrible like I am defaulting on my account which is totally the opposite. I now have unpaid charges on my account which totals to R600, I do not think that I should be liable for it. Can African Bank rectify this error that they committed, give me a letter to say I didn't default and refund the charges. I do not want this to be repeated.