Hi H8disconnection,
Are you able to try the following troubleshooting steps which are specific to NBN connections and see if this helps.
Another article you may find helpful is this one on How to optimise your gaming performance As you are using an NBN service 'Changing your Line Profile' will no be possible.
Also it is important to keep in mind when using test tools, any tests that conducted from a traceroute or ping is considered low priority traffic and as such will reflect increased response times as other traffic is prioritised, or the ping packets dropped from the queuing traffic.
See if this helps.