MTN continuously overcharging

I upgraded my contract with MTN in July 2019 where I agreed to a contract that would charge me R709 per month. It was only in January 2020 when looking at bank statements that I learned that MTN had been charging me R947 EVERY MONTH!!! I went into MTN stores multiple times to try resolve this and each time was told that it would be fixed, only to be charged R947 the following month again. After many fights on the phone it finally seemed to get resolved, however now I see that i have been charged R788.48 for April and R853.00 for May 2020. Do MTN just lie to their customers about how much they will debit order per month? Trying to rectify this issue month after month is just ridiculous! And each issue takes 3 months to be fixed, just so MTN can slowly start over charging again. I'm at the point where all i can think of doing is cancelling my contract.