Unfairly forced to continue with Vodacom Contract

I am so unhappy with the way Vodacom is treating my business. For the past 5 months I have been trying to cancel an upgrade on a contract but they can't assist, instead Vodacom is unfairly forcing me to continue with a contract even though I have returned the devices 4 months ago. The continue to to bill me for something I don't have and don't even use. Their system is so *********** because they can't even revert back to me. Everytime I call, they say it will take 2to 4 days to resolve , but they don't come back to me. Now they have blocked all communications so that I don't keep asking them as when are they cancelling the contract. I believe it's a deliberate act to force me to continue with the contract.