That means that your NBN connection isn't working and the modem is in LTE backup mode (the phone should still be able to work in this mode). What colour is the Mobile Mode and Mobile Signal Lights?
You could try rebooting your modem and see if your NBN service reconnects.
If that doesn't work, you will need to report the problem via 1800 834 273 or via Livechat.
Never be afraid to back yourself when trying new things, just always make sure you have 3 escape routes if things go wrong.
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