30 days notice is one thing, insisting the line remains live for 30d is not the same.
Any ISP can cease with BTO the next day. They can charge me for the 30d - but they are already charging me for 8 months, so there is no need - but insisting the line remains active is for one reason and one reason only.
So they can incessantly call me to try to persuade me to stay. I've received 3 calls so far this morning.