tombuster
Hello, welcome
Are you attempting to use the GOS phone app to get visual voicemail? (This works for me fyi. It is possible on many carriers)
Anyway, try this:
hold your finger down on the visual voicemail app for a few seconds > app info > force stop the app > storage > clear data & clear cache
settings > system > reset > reset mobile
Let us know if that works.
You might have to get tmobile's My voicemail app.
You could contact your carrier about the requirements for using visual voicemail, maybe there's a misconfiguration on their end?
Let us know how it goes!