I am having the same issue. My phone gives like half a ring and then goes to voicemail. I have waited on hold for chat and phone support for several hours multiple times and finally I have to hang up or exit because after 3 hours of waiting I have other things to do in my life.
Every time I have an issue with my Xfinity services that need me to call for support it is the worst support I have every gotten from any company.
I went through the whole ordeal. I tricked them calling business and was able to speak to alive person. He was very cordial and helpful. The problem was with the NOMOROBO calls. I went ahead and discontinued the NOMOROBO and then activated it again and so far it is working.
You are a life saver. I thought about re-enabling NOMOROBO after I disabled it but I thought I should leave it disabled until the issue was fixed as I did not want anything to interfere. I just reactivated NOMOROBO and called myselft and it rang normal.