Flactuating debit order amount

Good day I am a client in mobile contract with MTN mobile network company in South Africa. Between the 13th August ,2024 and the 17th, August, the MTN consultant called me to make me aware that I need to upgrade the contract because the one I am in has come to an end. I then told the consultant that I will come back to her, I just needed to check on the phones that I will choose from. On the 22nd August, 2024, I called them and upgraded my contract, I then asked to be transferred to the Accounts department to check if there is any outstanding balance, the lady in there told me there is no outstanding balance, and I asked about any Pro-rata amount I am about to pay on the new contract, she said there is no Pro-rata. On the 15th September, the debit order was the same amount that I was paying for the previous contract. On the new contract, The debit order is suppose to be R349.00. On the 15th October, 2024, they took R472.13 debit order amount, I called to ask the consultant about the extra R123.13, she then said maybe it is the Pro-rata. Today in the morning, MTN debit order taken from my account amount to R513.00. I called and asked to be transferred to Accounts department for clarity, the Accounts consultant told me that according to what reflects on the system, I am being billed for the previous contract phone and the current contract phone. I asked her to transfer me to the Accounts department management as she does not have the full information on how possible is that happening. She then told me that she does not have the authority to do that but she will send the e-mail to Accounts management maybe they will call me back before 17:00. Can I be humbly assisted in this regard as this exploitation is recurring and becomes a norm and it is quite irritating. To make things easier My account number is ACC BA***