Contract paid : But still deducting my account

i can never advise anyone to take contract phone with MTN, i had a contract with them. october 2019 i finished paying my contract. on November they deduced on R175.54 on my account. i called them they said they are charging me for the sms+350data. i understood that i requested the cancellation department to cancel. agreed . on december again they deducted an amount from my account. i reverse the the debit because i'm not owing them anything. now i'm busy receiving an SMS : Yello MTN still hasn't received payment. avaoid legal action by paying R175.54. Billing profile BA***. i called MTN 11/01/2021 enquiryng regarding the sms i'm getting they confirm with my number *** nothing outstanding. no one can tell me why am i still getting this sms. cos nothing is outstanding. but every month they want to deduct for something that i'm not owing