Hi @zhanyuma . When you got NBN, did you do the connection yourself or did a technician come and do it. If a technician did it, he might have disconnected the other sockets.
With NBN, do not use the ADSL splitter. Do not connect anything else to the phone sockets. Only the NBN modem.
When you put the NBN modem in another socket, what lights come on? Takes up to 10 minutes.