Vodacom dishonoring contract deals

I have logged a complaint with Vodacom where they decided to change my contractual agreement with them to pay a discounted rate as agreed to for a 24 month period. Vodacom's package price increased and they are now billing me almost a third more to the agreed upon contract price with the discount. I was about to cancel my contract with Vodacom when I was made a discounted offer for a 24 month period to remain with them. Vodacom's contract pricing went up and now I am being charged for this, which is not part of our agreement. When I logged a call regarding this with Vodacom, I received 3 phone calls in the period of 2 weeks where no one could assist me regarding this, and every consultant escalated it to a new department. It has been over a month later, and I was billed with the additional charges with no feedback from Vodacom. This is unacceptable and plain arrogant of Vodacom to bill me and give no further feedback in the hopes that I will just be fine with their breech of contract hoping I will just accept it. Vodacom says I may cancel my contract with them if I want but I will have to cover the penalty for cancelling the contract. What penalty does Vodacom get in all this? Why can they adjust the contract when and how they feel like and I still have to submit to a penalty. Besides dropped calls and poor data transfers, Vodacom is dishonoring their package agreements.