This is especially effective if you happen to get a human (increasingly rare).
We get calls about supposed credit card problems. "Oh, yes, I'd like to help. Which of the credit card holders are you trying to reach?" Not one robocaller has yet had an answer.
"Who is calling, please?" us also very effective.
Or just ask if their Mother knows they do this for a living. That guy CALLED BACK to cuss me out, and he might have been crying.