Or, if you need to cancel your service, make a short phonecall informing them that you are cancelling your service effective immediately and if they attempt to charge your account again, the charge will be contested and complaints will be filed with the Better Business Bureau. Then hang up.

You don't actually need their permission to cancel your service with them at all. You shouldn't be ASKING to cancel your service, you should be TELLING them it's cancelled. If they continue to ask questions, that is their business, hang up on them.