How to block all non-verified phone numbers on Xfinity Home phone service?

How do you block all non-verified phone numbers on Xfinity Home phone service?

None of the options listed in Xfinity Voice features that control nuisance and spam calls are effective at stopping non-verified phone numbers. Since the spammers/spoofers are using phone numbers of the area code of the Xfinity Home phone number, how to block ALL phone numbers from that area code? I know few people in this area code and those that I do know have my cell phone number.

Due to the lack of effectiveness of the options at the above link, I have litterally unplugged the phone from the gateway.