No Jehovah's Witnesses stickers
If you want Jehovah's Witnesses to stop knocking on your door, you can tell them verbally or you can also put a "No Jehovah's Witnesses" sticker on your door. They will be legally obliged not to knock on your door. You can order these stickers on websites that sell them or you can make your own using softwares such as Microsoft Word. You need an ordinary printer and labels you can buy in many stores. It's easy and cheap.