They are still ringing but now if you ring back there is a Telstra message to say the number has been disconnected

Calls. No-one there after picking up. Just silence and then hangs up.
Assuming it's an auto-dialer.

Will cold call you but will not talk or if you do not answer the call they will not leave a message. When you ring back the call remains unanswered.

Here is another nuisance caller... If you answer (which I should know better then to do) they will hang up on you, or at least some automated system does. Very likely the same people using (07) 3339 8011 as has same complaints.