Welcome to TPG Community!
We were able to locate your account using your community details and understand that you've contacted our Tech team to report the issue.
The error message that you received means that the router is trying to communicate to the NBN server, however, in your case the settings or configuration on the router was incorrect which is why the service is not working. This means that the router was reset to its default or someone changed the settings.
Our Tech team helped you with the configuration and the router was able to reclaim the internet.
In case this happens again, you may check the article that we've created that will guide you on how to configure the router manually. How to set up TP-LINK C1200 modem for Windows 10
Let us know if you need further assistance.