Did you book the flight using points from Qantas Frequent Flyer ?

If so, as per the T&Cs ( https://www.qantas.com/fflyer/dyn/program/terms ) , there is normally a 6000 point cancellation penalty

If this was an award for travel on Jetstar and you failed to cancel before the flight departure, then there is no refund ( see clause 14.3.9 )

If you booked using another scheme's points , then you need to check that scheme's T&Cs