iPhone incoming calls not working

When someone … anyone … tries to call me, I get a call banner for half a second that then disappears. The caller is forwarded to voicemail, but told that my voicemail isn’t set up. Verizon was completely unhelpful. I reset all kinds of settings and even restored the phone from a backup. Still having the same problem. The only thing that has changed was 14.4.1.

Anyone have anything similar?