I have had this problem for at least 2 weeks. I have tried calling or using several of the chat support options and I am sick of waiting several hours without getting any response. How can a huge company like Comcast have such horrible support?
Apparently it was NOMOROBO causing the issue. I deactivated the service but the issue still happened. Another person that had the same issue said they deactivated NOMOROBO and reactivated it and then the phone worked.