You could try fitting a sign 'no cold callers' to your door. I have one. It occasionally appears to have an effect. Last week two dodgy looking types turned up, read the sign (one of them pointed to it) then the other rang the door bell anyway.
I was sitting in my lounge and caught the eye of one of them so I just looked away. Eventually they left after posting an envelope through the door.
Turns out it was some religious claptrap. Apparently they think their sky fairy requires them to ignore the specific requests of others. Pity there's no commandment 'thow shalt not bother people who'd rather be left alone'.
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Andrue Cope
Brackley, UK