So you can ignore their letters and if they come to the door you can tell them to go away. The onus is on TVL to prove you are breaking the law to the court which they will never be able to do as you are
TV Licensing enforces the BBC's statutory obligation to ensure that every address where a television licence is required is correctly licensed, but its agents have no special rights and, like any other member of the public, rely on an implied right of access to reach the front door. The occupants of a visited property may deny an agent entry to the premises without cause and are under no obligation to answer any questions or enter into any conversation. If an agent has evidence that television is being watched or recorded illegally but is denied entry by the occupants so that (s)he cannot verify the suspicion without trespassing, then TV Licensing may apply to a magistrate for a search warrant, but the use of such warrants is rare.