Don't reply to any more.
Not replying to subsequent ones is not uncharitable. The other party just needs to learn that a "no" means a "no". Now, on the other hand, when the Jehovah Witnesses come to my door, although I really want to tell them no, I instead invite them in saying: "Well, welcome folks, you've come at a good time! I was just going to start praying the Rosary. Please join me!!! We can talk about your stuff, after that." Guess what, they NEVER come back