It sounds like there is a fault in the setup.
If you are unable to use it and they have been unable to resolve the issue for you, you can call 1800 TFIBRE (1800 834 273) speak to the NBN Assurance/Faults team, let them know this has been ongoing and request that they provide you an interim service until your service issues are resolved.
Depending on the situation this interim resolution will be generally speaking be either to redirect the landline to your mobile or to send you a temp mobile to use as an interim service but they have a range of interim solutions depending on the entire situation.
If you are unable to use it and they have been unable to resolve the issue for you, you can call 1800 TFIBRE (1800 834 273) speak to the NBN Assurance/Faults team, let them know this has been ongoing and request that they provide you an interim service until your service issues are resolved.
Depending on the situation this interim resolution will be generally speaking be either to redirect the landline to your mobile or to send you a temp mobile to use as an interim service but they have a range of interim solutions depending on the entire situation.