First stop is try and cancel with Vodacom. Under s14 of the CPA you are allowed to cancel any fixed term agreement by giving notice of your termination to the supplier 20 business days before the date you want to cancel. If you cancel under this section Vodacom is entitled to charge a reasonable cancellation fee, and can charge you for the full amount of any goods you received as part of the contract (like a phone).
If you are unhappy with the cancellation fee (you think it is unreasonable) or you they refuse to let you cancel you must lay a complaint with the NCC (0860266786 ).
By the look of your post though you will want to try and cancel on grounds that they have not provided adequate services (s54 of the CPA). You'll need to check, but it is possible for suppliers to contract out of this specific provision. I'd still try and cancel on these grounds though, and if they give you issues lay a complaint and see what the NCC says.