Are these real people on the phone or a recording?
My mother hates telemarketers and if one calls our house, we never hear the end of it.. So i am constantly bickering with her to just hang up the phone..
Well, last time someone called from the house with no steps asking for someone named John (who obviously had the phone number before we did as we moved house and got a new number), no matter how many times my mum told them noone called John lived there, the woman wouldn’t let her go, so I guess listening to what I had told my mum, she said “ok ill get him for you” and walked into the laundry and left the phone on the washing machine.. my sister walked in there 10 minutes later and the lady was still on the phone waiting…
Just a thought 
I think if you do that a couple of times they wont call back