rings and hangs up

Yep, rings, hangs up, annoys, mission accomplished

Rings. Unknown caller. No message left.

This is one of those robocalls that starts with a long pause, then "emily" comes on the line and says "Sorry, I had a problem with my headset" ... this is the latest version of that robocall that tries to know if a human is on the line and listens for responses. VERY VERY DANGEROUS. Hang up immediately.

How do I block these robocalls??  I keep getting them...!!  Very annoying to say the least.