Welcome to the community!
If you wish to use your old modem from Telstra you will have to configure it manually.
I went ahead and tried to use your community details to pull up your account unfortunately no match.
The steps of how to configure a modem/router will depend on its manufacturer.
We posted an article about the general setup of ADSL2+ connection.
You can use this a reference to configure your 3rd party modem/router.
Please visit this Link.
Let me know should you require further assistance.
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