Visual Voicemail Does Not Work

Visual voicemail does not work on my wife's iPhone SE (2020). We've reset the password, talked to AT&T support who recreated the mailbox, etc. Nothing works. We've done all their voicemail help guides.

Nothing.

She can call into voicemail, but Visual Voicemail will not work. 

We're paying for it but can't use it. Any ideas on how to fix it?