iPhone Voicemail Asks for Password Reset Every Day

Starting about one month ago, when I attempt to access voicemail, my iPhone 11 displays a message that my voicemail must be set up, and to enter the new password (twice). Once I do that, I have to confirm the message setup and then it displays my voicemails. My custom message is remembered, and old voicemail messages are displayed once again.

I don't know if there are any missed emails during the period that the voicemail is not showing as active.

How do I resolve this problem? Thanks