worst service provider

I have a contract with MTN for my phone., it has 3 months left. in August I received a call from a MTN third-party (Rewards, consultant name : Anita Pillay). She then advised me about migration of which I specifically told her that I don't want any changes on my profile, no extras , nothing i just want to pay it off and close it. she then said nothing will change , but to my shock, I received an sms from MTN saying i owe them R533 and must pay to stay connected. I had already logged a call with Rewards(Mondo) but no one is assisting me, yet money is being demanded. MTN is the worst network ever. how can they allow a third party to temper with a client sensitive information like this? my information is not protected by MTN as their client (POPIA act does not apply to them it seems)...to this day i'm still not assisted. when i call REWARDS(Mondo) they put me on hold for more than 10 minutes until i can't hold no more.