@Melb_cplThis is a long shot, Have you tried resetting the Arris? Use a paperclip or a pin that you use to remove a Sim Card Tray, hold it in for at least 10 seconds.
If the reset does not work, you will have to contact Optus Support and explain the problem. Optus will raise the issue with NBN and arrange for a replacement.
The Optus staff that are part of the Yes Crowd cannot access account details so they cannot escalate this issue for you.