They started an upgrade on your tower according to the Virgin Mobile network status page. I checked the Optus network page however like most things associated with the new Optus website it doesn't work for me.
It might work for you: https://www.optus.com.au/about/network/service-status
As mentioned by @Yeldarb, there is currently an upgrade occurring on the tower in Esk 4312. While we’re working on it, there may be some service interruptions but we’ll try to keep this to a minimum. Apologies for any inconveniences caused.