What should I do if a cult member comes knocking on my door?
If members of a cult like the Mormons or Jehovah's Witnesses should come to your door, you would be very wise to simply tell them you are not interested in their organization. Far too many Christians think that arguing with cult members is a productive way to exercise their witnessing skills.
You need to realize that these people have come to your house to save you. They didn't come for you to save them. Your chance of successfully turning the tables on them is about zero. If you have a burning desire to share your faith with someone, you should start with your neighbors or family members.
"Whosoever trangresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the son. If there come any unto you, and bring not this doctrine, receive him not in to your house, neither bid him God speed:For he that biddeth him God speed is partaker of his evil deeds"(2 John 9-11).