A lot of Witnesses want to be at your door as much as you want them to be there.
It's a high control cult that shuns those who disassociate or who are disfellowshipped, with children who are indoctrinated at an early age, so many members suffer in silence because they don't want to tear apart their families or friendships.
The whole questioning thing is actually part of predesigned presentations that are sent from headquarters in New York. They are instructed to use those presentations for their literature.
If you tell them you are not interested, generally they will leave you alone. There is no reason to be discorteous or belligerent. You might still get a visit every few months or so because they have cities divided up into territories that they preach in at least once a year, so any time the territory you live in is being used, you can expect a visit.
But it's pointless, and actually petty, to antagonize JWs for coming to your door. They're only ever coming for one of two reasons...1. They believe and want to save your life. 2. They don't believe and are being pressured into it by family or friends.