I need some information about your set up. Make sure nbn ncd is directly connected to socket using telephone cable.
how many socket you have in your place?
how's socket condition? clean, dusty, corroded
have you tried to connect nbn ncd using different telephone cable?
if its old style socket ( 610 type) then have you tried with different 610 adaptor?
I have created ticket for our engineering team to assess your case due to remote test are failing, you will received update in 48 hours. We might need to arrange NBN technician for this issue but we will update you. ticket reference # 59717497