Cancellation of contract - Lack of seamless contact method for sim only contract customers

I have been struggling to cancel my month-on-month data contract with Vodacom for the past almost 12 months. To date they claim I owe around R1800 for a month-on-month R299 subscription. Point one, with a sim only contract i could not call (which is the only method for cancellation by the way to my knowledge) into the cancellation department i then went to request the cancellation through one of their stores in Alberton, which was not done and i have to take the responsibility for their inefficient and disjoined processes. They made it difficult to cancel so they can keep you in contracts unnecessary. Point 2, it was very interesting to see that a month-on-month contract of R299 end up being R1800 despite them seeing that the sim data was not in use, how does this contracts work? Is this how the giant companies again violating individuals consumer rights?