Breach in contract without any agreement

I'm not happy with the level of service such a big company gives. It's true when they say the bigger the company, the less the services given.

I'm am writing this regarding my MTN LTE contract. I signed up for a 500GB 10MB uncapped package in 2023.

Came this year MTN decided to introduce a fair usage policy which they then reduced my line to 400GB 10MB line.

This is a complete breach in my contract which none of the sales or customer service reps can help with.

It's been 3 months going up and down with MTN and no one gets back to me. No one wants to help. They all quick to pass me on to this department and that department and MTN Direct which I've taken the contract with cannot even assist and is completely useless.