Call but doesn't leave message. Or when I answer doesn't say anything. I called number back and I wanted to put through to an agent. Not sure what it's for but if they want to talk to me they should leave a message or say something when I answer.

They  call many times a day.  Leave no message.  I am on the do not call list.

Just because you are does not mean all junk calls will cease. It stops honest businesses and telemarketing only, not political, fundraising, surveys, debt collectors, or scammers. The calls you're getting fall under one of the categories and should tell you to avoid answering mystery calls in all ways.