STOP caller unknown

I have been getting calls from this number on average twice daily, very early and very late. I have never answered and they never even listen to the outgoing VM message, as far as I can tell. They have never left a message. I am also on the DNC list, and it is discouraging to read posts here that indicate that does not filter for non-profit agencies. On the other hand, the legit ones don't call this often. I wonder if anyone is really going after this scam?

Irked,  the  Do Not Call Registry does not filter or block anything.  It is simply a list of those who do not wish to receive telemarketing calls. Nothing mechanical or automatic.  A list provided to those businesses who wish to comply with the peoples request not to be called.   When you and everyone else get these unwanted calls,  I hope that you follow up with a complaint to the DNC or FTC  and become a part of the solution.

Received 11 calls in 7 days.  Called it back today and a young man answered- just said "Hello?"  ,  like he was answering a home or personal cell phone line.  I didn't say anything.  Just hung up.  I've been getting 2 - 3 calls a day from this number for about a month and ½. They never leave a message and calls come in morning,afternoon and evening.

Got this call 8:47 PM Pacific time 12/27/12.
I called it back and got a message "All circuits are busy now".
I hate these kind of calls - very irritating.