There is a website called no more robocalls or something similar. they make their money from ads. If you have simu-ring like I do with Vonage, you can have 2 additional phones ring whenever the Vonage phone rings. I have my cell phone ring and the robo site's number ring. If their servers detect that an incoming call is calling hundreds or thousands of numbers per day, they shut down the call after one ring. You can still go to the Vonage call list and see who it was but at least it only rings once. And it usually doesn't even ring my cell phone since they shut it down so fast. The robo site number is (866) 732-6184 So I plug this in with my cell phone. They call my house land line with vonage and it rings once and robo kills the call. I'm sorry I can't recall the official name of the robo killer site but you can google it. My vonage id list said this number was "SURVEY". If it helps, Vonage allows you to kill or block calls that have no ID info. If it says "unavailable" or "unknown" or similar, vonage will block it for you.
Didn't recognize, so didn't answer. The majority of scammers-spammers need to verify a live person on the other end. Once verified by your voice they'll proceed with unwanted spam-scam calls in the very near future.