My voicemail doesn't show up and I cannot access it. What happened?

What happens when you try to access it?

I understood that part. When you go to VVM, what happens, an error message, etc? Voicemail is a carrier function so I suggest contacting them to sort it out. If the carrier needs to reset anything, including your password, they should be able to tell you.

VVM is visual voicemail. Your carrier has to support it on the iPhone. Check with your carrier about your voicemail problem.