Phone them up and say you no longer need one. They'll ask you the normal ****e, but just tell them you don't watch live TV....you watch dvd's, Netflix and YouTube.
If anyone comes to your door, just shut the door.
They have as much right to come in your house as the postman or milkman does...zero.
You could go one step further with them while you're on the phone...remove all "implied rights of access". They can't even come on your property then.
Once you've instructed them, you should get a letter of confirmation which is valid for 2 years. They aren't allowed to send you further letters in them 2 years.
They will say they have "other means of detection"...they don't. They rely on knocking on a door and being allowed in.