Incorrect billing date

When i took out the data line i signed for the debit order to go off on the 20th of each month. In June my account was debited on the 19th which is incorrect and the bank charged me R90.00 for that due to insufficient funds in my account. I called in to the call center to get clarity,spoke to Xolisa and Yvonne who could not assist with this. The two ladies didn't have any knowledge on how the billings system works. All i want is to refunded the charges i incurred for your guys mistake and to fix the debit order date.