MWEB changes contracted terms of R399 Uncapped for 12 months unilaterally to R449

I was totally taken aback when I received an email Monday 30th November from MWEB advising that my contracted R399 Uncapped package which is only a few months old will be increased to R449 wef 1st January 21. Never before have I had a contract changed unilaterally like this before. Not with any other service provider such as Vodacom or Telkom for that matter. How is this possible. Please revert back to the amount I signed on for which is R399 for 24 months