Rang me. I didn't answer. No message left. Rang the number and got "Optus advises this number has been disconnected ...." Has to be a scam if they don't want you to know who they are!

I don't answer numbers I don't know (for this reason), and they didn't leave a message.

I agree it's a scam. I answered with "hello" for an unrecognised No. & got a voice with probably Indian accent saying "I am John speaking, who am I speaking with?"
My response was "you rang me, you should know" & they hung up.

This number just called my wife on her mobile asking for her. When I asked who was speaking they hung up. I called the number back on our landline but all we got was:
"This call can not be connected, please check the number you have dialed and try again".
I'm calling this one a scam.