Contract renewal rip-off

I had a contract with Cell C for 2 years. Unfortunately they do not offer the plan anymore and had no other suitable plan. So I called in the cancel the contract to move to a different provider (this was late November/early December). They forwarded me to the customer retention center, where the consultant made me an offer whereby I would have gotten 990 minutes per month at slightly less than what I was paying before. So I agreed to this. It actually worked for the month of December. Unfortunately I did not see the invoice for January and noticed with the February bill that I only received 90 minutes and had to make a plan to pay for the extra minutes. I reported it to the call center and the agent said that they would investigate. I didn't hear back from them for about 2 weeks, so I called in again. I was told that the investigation showed that I renewed the contract in the Canal Walk store (which I did not - I signed up there for the original contract 2 years ago), but whoever is investigating would update me shortly. A few weeks later I still haven't received any feedback and I am still sitting on 90 minutes for the month. This is a proper *******. If Cell C doesn't want to honour what the offered me than I would rather have the contract cancelled, like I originally intended on doing, and move to a different provider.