They're offering you a service, they have the right to cancel it any time. It will be in their terms and conditions. As long as they refund you for the time you haven't yet paid for, there's very little comeback against them. This is even more relevant if you're paying monthly as you've not yet paid for the service they're taking away
Insurers will usually give you a window period of a couple of weeks to either pay them more or find other insurance - if the extra is competitive, then stay with them, if not then shop around some more