Overcharged and adamant billing is correct

I switched from ADSL to LTE on the 24 August. I was charged for the ADSL and LTE. The statement showed the reversal but the debit order took that went out of my account included the R239 for ADSL I called the billing department and they assured me that it will be reversed and I will be credited this month. I received my statement and seen that it was not reversed. I phoned the billing department again only to be told the amount is correct and that they did refund me. The lady refused to understand that the amount showing on the statement was not the amount taken out of my account last month, it was R239 more. Firstly how does the debit order not match the statement amount since the statement was correct, yet the debit order was not. They need to relook at their billing system.