If you are in Victoria, you should be using the comparison website every year:
https://compare.energy.vic.gov.au/
It will find the cheapest plan based on your usage over the past year.
In general, you can usually lock in a rate for ~12 months - after which point in time you will switch to the default rate (which will be higher, but is still capped versus how bad things used to be).
A Wild Matt-o appeared!