3 approaches: passive, active and vindictive.
Passive: just hang up and try to call block if the calls are coming from the same number.
Active: Notify your local police. Many now have scam units and this scam has gotten quite a bit of attention lately. Alternatively, when you recognize what the call is, just announce, "This call is being recorded for submission to the [your county name] District Prosecutor."
Vindictive: Get out your police whistle and keep it near the phone. Keep speaking softer and softer to make them strain to hear you and then give a mighty whistle blast into the phone.