Unfair Contract Expansion

I've been an MTN client for a while, I've had a really bad recent experience. My phone contract was increased without my permission or approval, and I was never properly notified about the change prior. I had no previous notice, no explanation, and no chance to accept or reject the new terms, so I only learnt about the hike when I saw my new bill. As a paying customer, this is quite annoying and feels like a betrayal of trust. This is made worse by the fact that all I want is fair treatment and openness, not even the cancellation of the contract. I've attempted to get in touch with MTN support, but I haven't yet received a clear resolution or a satisfactory explanation.