both my wife and I have the same problem. Both on the same Optus account. Both recently came back from New Zealand. I have done all the resets on my phone that Optus suggests, but they are still not working. We had both purchased Roaming Passes.
Just to be sure, you've tried a Network reset?
Network reset for iPhone/iOs
1) Launch the Settings app
2) Tap General
3) Tap Reset
4) Tap Reset Network Settings
Android instructions are similar but can vary between manufacturers. You'll just need to Google the name of your phone along with "Network Reset"