i have an NBN connection as well. Try resetting the black ntd (press the pinhole on the back of ntd)as it works most of the time. make sure the cables from the wall socket to the black ntd and ntd to the modem are securely connected. if nothing works then you can call 131423 option 2 + 1 for further checks.
If you are connected to wifi try to read this link as it may help :
Welcome to TPG Community!
I checked your account and was able to detect that your modem has been connected to the internet for more than 2 days now. It seems that the issue is not dropouts, but possible slow internet connection only.
Please try to check the link that was given by @firstknight for guidance. You can also check this Troubleshooting a slow internet connection link for more instructions on how to resolve the slow internet connection issue.
Keep us posted if what will happen and let's see what else we can do.