What is going on with the iPhone Visual Voice Mail?? People are telling me they called and left a message, but no messages are showing up. I have the 11 Pro Max and all my software is up-to-date

What is going on with the iPhone Visual Voice Mail?? People are telling me they called and left a message, but no messages are showing up. I have the 11 Pro Max and all my software is up-to-date.

I have tried setting up Visual Voicemail several times. It was working a week ago and just stopped and started giving me a msg that I need to set it up, but it won't accept a new message.