Bad Customer service and *****ing from customers

I have a contract with cell c and agreed on debit order on the 28 of each month, last month I changed banking details and transferred my payment on the same date of debit order into their account and they charged me penalty fee of extra R70 and I asked them to remove it because the money was paid in on time just different type of payment method, I did not default on making a payment I just paid using different type of payment method and both two consultants that called me did not want to listen to my side they kept on insisting that the charge will not be removed, I am being charged for I DID NOT PAID VIA DEBIT ORDER, is that way of doing business or treating clients, at the end of the day I paid and on time and provided proof of payment, this is really ridiculous and upsetting and ripping people off