Mtn billing problem

Im a mtn contract client for more than 20 yrs on 8 February i did do a contract downgrade on my contract from R219 to a R169 for 36months as from the end February 2023 payment doesnt show R169 as signed, i still pay R219 up to R232 pm there was a lot of communication regard my problem to solve the amount because i pay more than my contract i signed for R169 pm. Every month they will fix the backend and give me credit but up untill now nothing happen. This is the 3th contract i struggle to solve with the same problem because they over charged me everytime.