For newly installed NBN service, we did an article that you may find helpful.
In the event that you successfully set up the NBN service and still not working you may check if there is an ongoing outage affecting the service. See this link for reference How to Check for NBN Network Outage.
If there's no outage, you may perform basic troubleshooting step available in this article Troubleshooting no internet connection.
Should you need further assistance, feel free to search community for help or chat with us at https://www.tpg.com.au/support/contact/ and we'd be glad to assist you.