Unknown numbers

No, unknown means no information was sent. You could get a phone with smart call blocker or a third party blocking device that claim to block unknown numbers.

We are having the same problem! We just switched from Cox a little over a month ago. They supported NomoRobo, and we never had such a bad problem with robocalls as we have had since switching to AT&T. I also tried using the *77 feature that supposedly blocks unknown callers. Last night the calls from "Unavailable/Unkown number" started non-stop (5 calls in 45 min), leaving a message from "Amazon" on our answering machine. We finally had to unplug the phone to watch TV in peace. This morning there were ELEVEN messages recorded to voicemail in the space of 1 hr and 10 min. Already this morning there have been 2 calls from this number. We cannot live with this, but I am not willing to give up my landline. Unfortunately, for now, Cox is no longer an option for us; but I am really unhappy with ATT's phone service in regards to options for call blocking.

Have you gone into the phone features and set up your digital call protect?  I don't know if you can still use nomorobo with AT&T digital service or not. *77# is for call where the calling party blocked their outgoing CID anonymous calls or private call not for Unavailable/Unkown numbers Select call features in this link

After searching the website for solutions and after posting this comment, I did find information about Phone call protect, which sounded like what ATT used instead of Nomorobo. Problem was, I was following the instructions that were on the website, but every link I clicked on just sent me in circles and ultimately back to the same screen with my bill info. My screen options just didn't match the instructions. I could never find the location to turn it on. I ended up calling, sitting on hold for a really long time, but eventually someone turned it on for me. Let's hope that solves the problem. So far, so good.