Has the NBN been activated at your premises yet? You should of been given dates.
Go to http://10.0.0.138/> Advanced > Broadband.
If it says ADSL then go back to basic mode click broadband, and check to see if it has newdsluser@bigpond.com as the username. If so, change the username/password to your bigpond details.
If it says VDSL then contact NBN assurance and get them to check the connection