Change of debit order date

I have been requesting my debit order date to be changed for months now. NO LUC**** I was assisted by a Nkosinathi who had confirmed that the change was done and all was in order. To my surprise...I was debited incorrectly once again this month. This is highly frustrating as I incur additional bank charges due to insufficient funds when this transaction is processed. I’m not sure how to proceed if I can’t be assisted by the bank itself, the call centre is forever busy and it jut takes long for one to get through...I really hope to get a response!