My Visual Voicemail Doesn’t Exist

I am on my 7th iPhone, and my visual voicemail doesn’t and has never existed...

I click on the phone app, go to the voicemail tab, and the only option I have is “call voicemail”, and the rest is a blank screen.

Ive followed all of the troubleshooting available on both my carriers (Telstra - Australia) and apple’s websites.

Ive restarted my phone, I’ve followed the “Set up Visual Voicemail on your iPhone”, and have the current update.

After following those troubleshooting steps, I’m still not able to use visual voicemail. I’ve contacted my cellular provider, and my account has always been fully enabled for visual voicemail.

I AM AT A LOSS!

My carrier told me to contact Apple... so here I am - desperate to get some answers!

Also, if I go in to change my voicemail pin, I get a pop up saying “Voicemail Unavailable, try again later” however when I ring voicemail I can listen to my voicemails, and have never had to put a pin in to hear them...

PLEASE HELP!!!!!