My caller ID showed an Unknown number with no message left.  Therefore, that = telemarketers and or scammers.   Most of these are "robo calls with spoofed numbers," so reporting them does no good.  NEVER give or verify personal, credit card, bank or financial information to ANYONE who makes an unsolicited call to you!!!  I "block" these numbers if they keep calling

A man's voice leaves a message on my machine sometimes twice a day asking, "is Melissa there? Hello. Are you there?"
He used to ask, "is Charles there?"  It's every week.