Have you tried to connect a computer/laptop directly to the NBN NTD and use a direct broadband connection.
This will tell us if the issue is coming from local network or NBN network.
If the speed is good on a direct NBN NTD broadband connection then it means that the issue is coming from one of your devices.
There's no tricks. It's just a simple stuff to diagnose the issue properly.
The idea is to take away the router and other devices that may cause the issue.
Because most of the time if not always, it's the devices on the end user's local network is causing speed issue such as auto update or auto sync system or app on other devices.
Connecting a computer or a laptop directly to the NBN NTD will eliminate the possibilty of your local network issue.
What kind of laptop to you have?
Is it MAC or Windows?