How to avoid a Jehovah's Witness (Pt 1)

A week ago I had a knock at the door and it was the Jehovahs witnesses. Now I think I'm quite a nice person and I hate people who just slam doors in their faces so I listened to what they had to say, accepted their magazine and remained courteous. They were really pleasant and I didn't mind speaking to them but the whole time I was thinking "please leave, please leave, omg my neighbours can see me stood here why don't they help me!!"
I think this panic was instilled by my mother who always got vexed when they would come by.
Long story short, I gave them my first name - well it didn't seem an unreasonable request - and then my phone rang inside, I apologized and said I had to go and somewhere in my trying to leave and grab the phone I made some committal noise to them coming back again....since then I have been EXTREMELY paranoid that every knock on the door is them. I don't want to offend or upset them but I don't want to join their cult religion either.