Random Price increases on a contract !

Loyal customer for 20+ years here. I am deeply disgusted that even with a signed 24 month contract, MTN can just unilaterally change the price and implement an increase without my consent. Apparently there's some clause in the contract that allows them to do this, but its still *********. We budgeted for a specific amount every month and now it's randomly changed. NOT OK! In which case why sign a contract? Just leave us on a month to month where you can change things as you please