Every time an ISP does that around here they send you a notification via certified mail with a prepaid return envelope and a service cancellation form included - you can decide to not continue using the service without any early cancellations fees etc.

If they fail to do that they get fined by consumer protection agency, are required to return any fees they charged based on the change and they get to start over - send a notification that follows the rules resetting the clock for those who opt to cancel