Thanks for passing on the details, @yafei253699.
I have modified your post since it contains your account information.
Based on the recent update provided by NBN Co, a network degradation issue is under investigation. At this point in time, we still have no new updates to report on and NBN is still looking into this network issue. We will surely be in touch once we hear from their team.
We apologise for the inconvenience caused.
Based on the recent update on your account, an Engineer has already been in touch with you and advised you that NBN technicians have been working on restoring your connection in the soonest possible time.
The assigned Engineer will continuously provide you with updates where possible.