Please check this link. Click Fixed Outages for NBN, Cable, ADSL and Mobile Outages for 4G/5G and enter your postcode.
If you are NBN customer you can also check here https://www.nbnco.com.au/support/network-status
If there are no reported outages, Please message Optus Support 24/7 from the My Optus app. If you do not have access to the My Optus app you can use social media to contact Optus Support, please send a PM to Optus on Facebook or a DM on Twitter and include in the message you do not have access to the My Optus app.