@kevinfanjie 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.
Phone 133 937 ignore the prompt to Press 1 and wait for the options. I have read the wait can be a long time.
What type of internet do you have, kevinfanjie?
What suburb/postcode are you located in? Have you checked for any known outages? Click on the Outages tab and tick the Fixed outages tickbox and enter your location to see if that’s the issue.
All things to check prior to contacting Optus.