MTN overcharging customers and not addressing the issue

I signed a new MTN contract at the iStore in February 2024. On my March invoice I noticed that MTN is charging me more than the contract I signed up for. Looking back at my previous invoice I saw that they did the same in February. I called the MTN call center on the 16th March. The consultant who took the call kept insisting my invoice was correct. He did not seem to grasp what I was explaining to him. On asking to chat to his manager, he advised that he cannot transfer the call, but that she would call me back. I received no call back. The reference number for that call is I-***. On the 18 March I sent a complain to MTN's complaint email address (***). I explained my issue, what transpired in the call, and that nobody has called me back. I even went as far as adding a screenshot of my contract to show them my contracted monthly amount, and a copy of my invoice so they could see what I was being charged monthly. I received an automated reply with a reference number 6ab62897-0d6d-40a2-838b-b7f54e521425. However, up till today, nobody has contacted me with regards to resolving the issue. I guess I will have to find out what my next steps should be legally to take this issue further.