Debit order

I have submitted a concern re the cost debited to my account fore debit orders not paid because of insufficient funds. <br> This is a business account and sometimes funds are not available on the specified date. BUT I have a longstanding relationship with Telkom and re submitting the debit order has always rendered the expected results. Instead incredible amounts are added to my account which are not justified. How is this cost determined. I expect these amounts to be reversed or I will have to re consider my relationship with Telkom which I do not want to do. Please help.