Thanks for coming back to us @JaneOlivia1 and all of your details are correct.
I have sent a new pin to your phone via text message, please let me know if you have received this and you're now able to access your voicemail.
Regarding your sim card, we have done a network migration and you would need a new sim card for us to update the network, we cannot update the network without a new sim card, this service but your handset should continue to work on the network until you return to the UK.
The other option would be for us to send a sim card to your home address and then you would need to arrange for the sim to be activated in the UK and sent to you in Australia.
The downside to this is that your current sim would be disabled and you'd have to wait to for the sim card to arrive.
Regards,
Steven_L