Likely using some sort of demon dialer program that dials in numerical order. My cell is unlisted, kept very strictly private, and on the Do Not Call list but I still get scam calls. Scammers are going down a numerical list; i.e., 123-456-7890, 123-456-7891, and so on. It's that simple.
I called the number back and it is a charity organization seeking donations. It will afford you the opportunity to be removed from the list. The recording continues to explan that because they are a charity organization they are exempt from the no call list. I removed my number so we will see if it works.
You have to call the number back and they offer to remove you from their list by pressing 1 then entering your number. I have gotten calls from 616-608- 1011 and also 517-679-0757, also from Michigan. Do this for both numbers. Hopefully it will work.