Useless staff and unauthorized charges

I have a contract with mtn for a number of years and in 2020 I relocated to another country. I wanted to keep my number that I have for long time and in January 2020, I activated an international sms only roaming, which went well for over a year till February 2021 when I start receiving calls from RSA. A service I have not activated and I informed mtn of this technical errors on their side. It took them a week to address and I received no more calls to find out that mtn starts to charge my account for international calls coming to my number. So far I called mtn 5 times to sort out this unauthorized charges with no success. Their so called service champions are useless and no basic skills to report queries and each time I had to explain same story. Its now two months with no feedback and I had to reverse all payments and cancel the stop order. More important I have to give up my number that I have kept for 20 years and get another number with vodacom.