MTN Business Forces Migration to Dissimilar Packages

I am on an old MTN Unlimited Broadband Lite package (previously MTN Uncapped Lite) and MTN claims that they can force me to migrate to another package. The current package that I am on is unlimited at R330pm (month-to-month as agreed in the initial signing) and their offer is 3gb at R79pm. They have given me a limited time to respond to an offer which is nowhere close to the current package thereafter I will be automatically migrated. Their call centre agents appear pretty much clueless about how this works and know nothing much than the basics. What the hell is going on MTN!!!. You cannot change terms of contract initially agreed to suit yourselves. I need to speak to SENIOR management please or I will take it much further!!!!