calls frequently no messages left and no respect for the time that they call. I received a call at 8:45pm.
who are they?

Received a call from this number a few times.  No message.  On the National Do Not Call Registry.  Lot of good that does.

Get calls from this number on my cell almost every day. Never leaves a message. Tried calling back and got a recording to dial the extension I was trying to reach or wait for the beep to leave a message. I waited, left a message telling the caller that if they called me every day and it was so important to reach me, the only way I'd call back an unknown number was for them to leave me a message telling me who was calling. The calls stopped for a week, but just got a new one today, June 20, and still no message.

I am pretty sure this number is used by charitable donation people.  If you ever gave someone a political donation for example you will get harassed continuously even if you are on the do not call list.  Political and charitable calls are exempt  from the Do Not Call registry regulations.

Also getting calls from this number. When I do not answer there is a disconnect with no VM. Based on prior posts, seems like a robo-dial call.