Telkom ways of generation more revenue

Telkom 10 day internal processes set to have a negative impact on debtors and driven to increase revenue. I switched banks and inform Telkom on 18th with the next debit order on the last day of the month. Telkom advised that I need to process an EFT payment as all the changes will only be effective in the following month. I paid my latest invoice due on the last day of April on the 23rd of April. Funds reflected on were later allocated into my account on the 24th. The customer service agent was advised by her manager that no debit order will be ran on my account as the account is cleared with ZERO balance. Little did she know that Telkom will still carry on and process the debit order even though the debtors account was Nil? The debit order was rejected by the bank due to insufficient funds. Telkom now wants to process a R200 rejection fee journal which will be an addition to my next invoice. It needs to be reminded that this was their own internal process which led them to process the debit order even though the account was in Zero balance due. Whose responsibility is it to allocate funds and clear debtors accounts timeously? Telkom or the debtor? For which period is the rejection fee for as April was cleared? Who is liable for the rejection fees at Telkom and at the bank? Why must a pay for their on the delay in allocating and reconciling debtors timeously ?