No voicemail.  Keeps calling

called 5 times in a row no voice mail

This number has called us, on our home phone line, a couple of times. No-one is on the other side, no robo call, nothing. When I've called the number, an automated female voice asks me if I'd like to be removed from their "do not call registry" (by pressing "1").

That's it. Nothing else. Not sure what this is about. Maybe it's a phishing technique used to verify your phone number is valid?

yes exactly. if you answer they sell the # to other shittbags

I didn't answer the call (I usually don't answer calls coming from numbers I can't identify), and they didn't leave a message.  Annoying.