Caller ID shows unavailable. I don't answer, they keep calling. We have been with the do not call registry for over a month now. Why would I be still getting calls?

They called me late last Friday, and then 1st thing on the next Monday.  Caller ID says "Sioux City, IA."  I think it might be related to all the harassing Redline Recovery Service calls I've been getting, coinciding with calls labelled "Jensen Beach, FL," "Texas call," "California call," and/or "Scholastic Inc" calls.  So much for the worthless Do Not Call registry.  I get 3-5 of these worthless calls a day, and none leave a message.  I suspect government officials don't get harassed like this.

We are on DNC registry and this number called but there was nothing other the other end when I answered it.

Received a call today from this number - no message was left.

Was called and answered the phone, no one on the other end.
I blocked the caller ID and called back i.e. *67 712 872-3351, auto answer: "Hi, if you are calling because you missed our call, please hang up now as we may call again soon with our special offer, however, if you prefer that we not call you again please enter your 10 digit phone number and we'll add you to our do not call list".