Cancellation Contract Nightmare

I cancelled my contract with MTN even paid the cancellation fee in July. In the month of July they deducted two times what I normally paid, and then in the month of August the same thing happened. Cancellation reference ***. I called customer services to resolve my issue they transferred me about 5 times and they ended up ending the call while I was on hold, I even went directly to the MTN stores close to me they told me that I don't exist on their systems I fully paid and cancelled my contract but for some reason they still deducting from my account. 2 days ago they threatened to take me to legal actions not sure why because I paid the cancellation fee they wanted from, one of the "Sales Champions" even assured me that I wont be paying anything, my contract is fully cancelled, they even said my number is on prepaid even on their systems