Calls Going Directly to Voice Mail, but Do Not Disturb is turned off

Help! I have an iphone X using iOS 13.3.1

Just 2 weeks ago, with no updates made on my phone that would have triggered it (that I can recall), anyone who calls my mobile number is sent directly to voice mail. No rings. The call is not even showing up in Recent calls!!

I called Apple and Verizon, and neither had no idea what was going on, and both said I should update my software, but whenever I update I get intractable sync issues on iCloud and god knows what other problems.

I tried a hard reset, and looked at all settings, but found no clues.

To top it off, it was intermittent in the beginning. I asked someone whose calls were being diverted to voicemail to click on my phone number in a new text message—and the call went through.

Non of the incoming calls are in Recents.