Worst service provider

I had a month to month router with mtn which I cancelled in January 2024. I kept getting billing statements after the cancelation which I did as per their direction and even returned the router to the nearest store. I enquired only to be told to go back to the store, which I did and I was told the router was collected 3 days after I returned it. The billing statements kept coming and I called and enquired again of which I was told that the cancelation had gone through but it will take a while for the system to stop sending. Now I got another email saying my service will be stopped and account handed over if I don't pay the R289. Which service exactly is referred to as I haven't been their customer since January 2024? Please whatever you do stay away from mtn,it's the worst service provider I have ever dealt with