This is a scam. Hung up when I answered. I called back immediately and says this number has been disconnected.

when I tried to call the number back 5 mins after receiving a call from that number, i had a recorded message from Optus stating the number is disconnected!

rang back got message number is not in service

The lady who answered was unable to tell me where she was from and just wanted to know if I was working. When I told her I work for Services Australia she promptly hung up on me.
On calling the number back “surprise surprise” the number is disconnected.