They're fun to play with ... One game is tell them you're interested but have something on the stove and you'll be right back... See how long they last
I've tried variations on that theme. Put down the phone and come back once in a while to ask, "Are you still there?"
In 2015 we switched our phone to TPG in 2015 (our Internet provider) and Teltra removesd us from their phone book. since then we get only calls from those companies that have old lists..