Visual voice mail unavailable. how do I get it back

My voice mail has a message

Visual voicemail is urrently unavailable

Call Voicemail

So now I need to call voicemail several times a day to see whom has called

I was on line with tech support last night and we got disconnected. The person left a voice message and I did not get it because I did not call voicemail.

What do I do

I swear the iphone11 is a LEMON and a total mess. Yesterday it called all the people that I had called during the day~~There are times I can not even answer my phone and neither can others-like the phone freezes--and my phone does freeze alot