These are illegal skip tracers not following FDCPA law.

Report each call to

donotcall.gov

Never engage with them over a phone. Never mention who you are. Always ask them for their name and their company name. Never give them yours. If they refuse, hang up or tell them you are reporting them to the FTC. Then report them to the FTC.

DONOTCALL.GOV

Don't be lazy, report them if they call you. Don't be lazy.

Got a call this morning when I was on another line. No message. But I've gotten in the past week multiple calls from different numbers where they got my first name right and then gave the wrong last name. I've started asking "Who is calling and what is this in regards to?" and get a vague reply. Numbers I've gotten these strange calls from in the last week include:
312-614-1338
804-596-1074
469-757-8869
719-219-7193
276-692-2049
415-366-0709

UPDATE:  Received another call, this time from a man with an accent named Charlie (!), who wanted to connect his boss with one of our IT managers.  Again claimed not to know the reason but would get back to me with it.  I won't hold my breath.

I got a call from this number.The person had an incorrect last name & were searching for information..

Called and asked for Greg, would not give last name. Finally asked for Greg Smith. I told her there was no Greg Smith ans that she had the wrong number. She then said, so it is Greg but not Smith as if she was trolling for the name. Weird.