MTN Online Upgrades

Dear all, I was recently contacted by MTN Online department to upgrade my contract. My previous contract amounted to R655.00 per month, and after the upgrade, it should have reduced to R499.00 per month. My first invoice after doing the upgrade amounted to R1303 and the second to R1240. I have trying since 16 October 2022 to get this resolved. On a daily basis one needs to call 4 - 7 times, firstly to speak to a "Service Champion" and then the line just gets dropped. I even attended the MTN Greenstone store, and was told that they are not able to assist. For some reason, every time an upgrade is performed on my account then MTN makes a mess of it. Can someone please assist to get this resolved?