iPhone 8 Plus voicemail stopped working abruptly 2 days ago - won't come back.

Hi: Turns out my voicemail stopped working a couple of days ago and "Calls are being forwarded to another mailbox"? I only found out about the issue when a friend emailed me. I've:

1) Rebooted multiple times.

2) Reset Network Settings.

3) Checked to see if I have the latest (Verizon) carrier settings - I do.

4) Toggled Airplane Mode and Cellular Data on and off multiple times, with reboots.

5) Even found a reference to having to set Siri up to VM to work - which I though was particularly specious, but I did set it up - and VM still doesn't work.

6) Temporarily deleted Robokiller app in case that was messing with me.

Nothing I've done so far is working. OS 12.3 (up to date apparently). Any thoughts, advice appreciated. Thanks, John