CAN'T GET OUT OF THE CONTRACT EVEN WHEN DONE PAYING, THEY'LL SUCK ALL THE MONEY FROM YOU.

I have requested for cancellation of my contract 3 months ago. I paid what was then an outstanding fee (arrears), but I still get billed for the services I don't use. The SIM is closed and each time I call MTN they say they can see that Contract is being cancelled.. so what Am I being billed for??