Anonymous Call Blocking lets caller ID "Not Available" through to ring.

Not necessarily blocked,  just so they don't ring through.  It would be OK to shunt them off to voicemail.

Thank you for that information. I would recommend checking out the Xfinity Spam Blocker settings. That may assist with what you are trying to accomplish. Here is some information on that feature. It would allow you to select different risk levels and have the calls sent to voicemail instead of just being blocked. Please let me know if this helps. 

I did read the material on spam blocker and I have tightened the settings.   At low, medium and high risk I have calls going directly to voicemail.  That doesn't help. 
The problem seems to be that "Not Available" is not classified by spam blocker as any level of risk.  Neither is a caller ID with only a city name.

We can try and look into this further.

Please send us a direct chat message with your full name and complete service address to “Xfinity Support”. To do so, click on the chat icon located at the top right of this forums page.

To send a "Direct Message" to Xfinity Support:

Click "Sign In" if necessary

Click the "Direct Messaging" icon 

Click the "New message" (pencil and paper) icon
The "To:" line prompts you to "Type the name of a person". Instead, type "Xfinity Support" there

As you are typing a drop-down list appears. Select "Xfinity Support" from that list

An "Xfinity Support" graphic replaces the "To:" line

Type your message in the text area near the bottom of the window and press Enter to send it.