xfinity land line sends known caller to voicemail without ringing

Callers that call regularly who are friends are going directly to voicemail. It didn't happen all the time, but now it's happening every day, and for my brother's number now every time. 

We've rebooted the modem more than once. 
We've checked that there's no forwarding or blocking. 
The phone works -- I get spam calls and junk calls too and some wanted calls
I tested it by calling my brother, asking him what he heard on his end. it goes directly to voicemail.I asked him to call back and his call went directly to voicemail.
I have no idea what to do at this point.