Just got a call. I answered and they hung up didn't say anything

Called me today at 1248pm. Only answered it because it said Michigan and I have family from there. Then I heard.."this is not a sales call..." so I hung up.

The number called my work and personal mobile numbers at 6:25pm EST

I called the number back and it gave me to option to be added to their do not call list.

got a call at 6.19pm EST on my cell, did not answer as I did not recognize the phone no, later internet search showed 213 as Michigan local area code?, I am sure that's got to be spammer/scammers or some sort. But, my number is not registered anywhere, so on a second thought this kind of phone calls from a no with one one to answer seems  like Telephone tower spoofing or one of those interceptors?, there is a lot bad going on in spying, spoofing, intercepting, hacking etc, by the so called agencies, hackers and what not...this number could be one of those?.

Called me today at 11:03 am - left no message