Thanks for being part of the AGL Community.
I would recommend checking the Help & Support pages for NBN on our website here. You can also find the contact details for our NBN team there, in case you require further assistance.
Once again Cheers Jenna,
I have confirmed with Tech Support Team, that if the modem is being factory reset, I have to ring them to reinstate the VoIP.
Lesson Learned: Don't factory reset modem.
I also used this feature get my settings back:
Settings - Backup
Backup Broadband Router configurations. You may save your router configurations to a file on your PC.