Hi bernie, I wouldn't worry too much about having them knocking at your door, it seems these letters are computer generated, they go through different stages and if there is no response from them sending them, it all starts again from the beginning! This site is good for info on how TVL work, http://www.bbctvlicence.com/ There is a load of the letters posted up, which they have been receiving since 2006!
Danielle
Emancipate yourselves from mental slavery; None but ourselves can free our minds. Bob Marley (Redemption Song)