Even still there would be no cause for legal action... what would the damages be?
They could simply shut off the service for the customer like every other service provider in the world would do...
Not every service provider works that way - I've seen plenty of hosting companies who just start charging overage charges - it would be stipulated somewhere in their TOS which most likely would also have the wording that it can be changed at any time. I'm not justifying the action - just saying that it does happen.
