Contract Cancelation

Since from January till date, I have moved from one consultant to another but with fail when coming to contract cancelation instead i get promises that i will receive an sms and email confirming that my contract has been canceled

Worst case, they have upgraded I receive data and airtime that I did not agree on, I sent emails to Vodacom regarding this but i did not get any help... On the 1st of April i received a call from Vodacom saying I owe a total amount of r850 which I know nothing of or even agreed on it

Now I have a debt on my name because of Vodacom refusing to cancel my contract