It's amazing that one-sided contracts like this (where you're committed to a term, but they're not committed to a price) don't violate consumer protection laws. What if they chose to double your monthly bill?
You sure? In NL it's just inflation, anything else means you have the option to cancel. Seems odd that they could specify an extra percentage in their terms of service just for the heck of it, not because of increased costs or so.
Though, in practice, you're with a carrier for a reason (either best quality or lowest price) and the competition also raised prices per inflation, or at least close enough that it doesn't tip the scale, so there's never a point cancelling a contract prematurely. Maximum contract duration is 2 years anyway iirc.
I had agreed to a price of £x per month. After 2 weeks, I hadn't even had my first bill in, I got a letter saying the price was going up because of inflation...
2 weeks!