Vodacom cancellation

Over the last 4 month, I’m trying to cancel my Vodacom contract (over 3 years old , way pass the contracted period), but unsuccessful. I was told I can only phone the cancellation centre. Then we I called two months ago, despite my clear instruction to change the contract to pay as you use, the agent still put me on another payment plan which I never agreed to. And the worst of all, the new monthly charge are R100 more expensive than my original monthly payment! This is actually *****! Vodafone, you do not have the right to collect the money when there is no contact with the customer!