The internet light is off when the credentials of the modem/router is in correct. Try to re-enter your TPG username and password to the modem/router. Let us know how it will go.
In the event that the issue still persists, send us your details via PM so we can proceed with the initial assessment.
I have plugged my own modem and router（2in1），and I have configured it follow your NBN settings. Power, DSL, 2.4G, 5G lights on the modem are solid green now except the internet light which is off，I can't solve this problem，I need your help （modem ：TP-Link Archer VR1600V）