Verizon iPhone ringing once and going to voicemail issue fixed by re-syncing calling line

For months, I had this issue where my phone would ring once and then go to voicemail, but if someone called back right away, it would then work. It wasn't Do Not Disturb, and Apple couldn't fix it.

So I finally got through to someone on Verizon support chat who was able to help me. What they did was re-sync the calling line to the database. This fixed it immediately.

I hope this helps somebody else because I have been searching for an answer to this for three months.

[Re-Titled by Moderator]