Spoof dialer... an automated system looking to see if a voice picks up and responds.... they hope to hear you say "Hello?". If so, that puts your number on a dialer list that is sold to marketers... This is how they make sure they are not dialing a fax or data line.
+1 (346) 239-6527 I just received a call from this number. They called my business line, I answered it and no one responded. Will add them to a blocked numbers. Not sure why if I am on the do not call registry I get these calls