Debiting my account before pay date

Std Bank debited my account on the 15th of December with R4550 being home loan instalments. Our agreement was that they can only do this on the 21st of every month as I only get paid on the 20th. I contacted the call centre and was advised to send an email giving the details of the complaint. Nobody contacted me. Again on the 15th of February and March Std Bank debited my account. Despite my efforts to contact the call centre and sending emails nothing has been done to rectify this error. In March 2015 I contacted the call centre once again and asked them to cancel the debit order as I was making EFT payments. I was asked to send a fax as they do not take debit order cancellations telephonically. I did exactly that. To my amazement on the 15th of April Std Bank once again debited my account . My credit record is damaged, and my bank is charging me for the returned debit orders. I am rather saddened and disappointed by how Std Bank has handled my complaint. They are showing complete disregard for the customer. Hopefully someone will respond once they realise that the complaint is on \hello peter"\""."""