I called back number (02) 6580 8200 reached IVR for a company called Holiday Coast Credit Union.

received a call from this number, no voice. Called the number back and it was answered as Holiday Coast Credit Union. I could hear the receptionist, she could not hear me and hung up.
I called back again a few minutes later and this time "Steve" answered and the line was good in both directions. The voice sounded exactly like the "Steve" who previously phoned and asked me to call 1300 365 724. I don't know how they got my number (I am on the Do not call register) and Steve suggested someone entered a wrong telephone number for a customer contact. Hmmmm...