Hi @Yu
You may disable/barred it via your TPG my account from below link
https://www.tpg.com.au/myaccount
To access your login you need your TPG Username and password
After opening of your account you will see left side NBN Home Phone Services below that you will see View NBN Home Phone Service Account so click over it so you will get access to NBN home phone tools then click over NBN Home Phone Service Control Panel so that will show you one form where you can see different option including call barring.
I hope this information can help you.
BasilDV
