I got a call from them and when I tried to call back, I got the number has been disconnected.

That probably means it is some kind of nefarious scam. Spoofing (providing a false) caller ID is not trivial and of no point unless the caller has something to hide.

I receiving unwanted calls on a allmost daily base from 312-951-7985 for a while alredy.
Phone disconnected when I call back this number. .....Very bad...
I am in the Not to Call list.

Got a call from 312-951-7985 yesterday.  No message was left in my voice mail.  I tried calling the number through my google phone account, and an automated message answered(may have been a google service though) saying there were three similar businesses, asking me to make a selection to connect to one of them.

zanga.com(or E-zanga.com) online advertising
College Quest
Advantage Health Care Partners