missed a call tried to call it back and it says a recording Optus wishes to let you know that this number is disconnected

Evil scammers trying to steal information or whatever it is that they are after.

Save yourself the trouble and block them at once.

I got a missed call from these guys but they left a voicemail that was just static. hm.

These F...ing morons continue to ring multiple times - where is telstra with this crap?
surely they get reported.

Same just no longer connected, how do we find out who it is?

Didn't call back. Googled the mobile ph number and saw above comments

I got a missed call (just 2 rings) from this number. Did not call back from my mobile but from a public phone. Got the same message "Optus wishes to let you know that this number is disconnected". Block this number. I have heard of many such spam calls. If you call back, it will be recorded that your number is actively used and that you can be spammed. Do not return calls from unknown numbers. People who genuinely need to contact you will leave a voicemail.

Rang once then went to message bank. Most likely a nuisance call. Another one for the blacklist.

I called back number 0439 839 780 rang once then goes to busy tone.