no response

In January 2015 I advised Std bank to change my debit order date from the 20th to the 25th of each month. Since then the date has not be changed. In March 2015 the debit order went off on the 20thi sent an email enquiry. The correspondance agent responded advising me that the notification to have the dbit order date changed was received, however due to a system problem the debit order went off on 20-03-2015. She advised on the email that goig foward the debit order will be temporarily stopped and in April I should make a direct payment. However again on 20-04-2015 Standard bank has debitted my account. This time there was no funds in my account and the debit order returned unpaid. This week I get a call from the collections department to enquire about the non payment. When I advised the collections agent of the situation she could not assist me. I have tried to call the call center to speak to a manager however I have had no joy in speaking to a manager. I'm am quite fustrated in trying to resolve this problem. Please assist me urgently. Kind regards Mrs S Chetty