It’s common to receive a mail from some service that they’re changing the terms and conditions of their service (internet provider, gmail, etc.) These changes are unilateral and can be about anything, from their privacy policy to the money they intend to charge me.
Why can’t I unilaterally send them a mail and say, I am changing the terms of my patronage and will now insert my new policy (pay only xx amount, or demand a mint Chico chip ice cream every Tuesday)?
At least in the UK, that kind of unilateral change also comes with a free contract break - if you don’t like it, you can quit without paying a y penalty charges.
You can probably try to do similar to them… They will just fire you as a customer.