For customers experiencing any issues with their NBN service, we recommend the best thing to do first is check if there's an outage on the NBN network.
We have created this article that can guide you on How to Check for NBN Network Outage
If there are no known outages in your area, customers can proceed with the troubleshooting steps indicated on this link : https://www.tpg.com.au/support/nbn-fttn/problems_connect_internet_nbn_fttn
In your case, there was a fault within the NBN network which was resolved. Your service is now working using the replacement modem that was provided.