MTN bad service

I am with mtn for years now Since 2023 june ive been struggling with mtn One of my contracts needet to be cancelled due too it was time fot upgrade but i didnt want too.. The contract was 170 something The next month they started deducting R550 for the whole of 2023 and 2024 the amount went up too 600 and something.. Every month i call mtn too make it right and everymonth they tell me the same story that the number is not on the system anymore but im still getting invoiced.. Every month i call but no difference mtn ows me more than R10000 ..I am out of options on what too do because im tired of calling all the time and they dont fix the problem..