Worst service

I have a month to month contract for uncapped wifi with MTN which I was told when I join I can cancel any time yoh what a worst experience I've had with the branch in overcity Durban Mtn I sent the device back and canceled the contract but money is still being deducted Ntokozo the guy who sold me product says it'll take a month for cancelation it's almost 2 months now still not canceled and the just taking money from my account for something I don't use I so frustrated I want to sue this company