0455 781 769 shows as the caller ID but this is spoofed. If answered, the call connects briefly then hangs up. Phoning the number back gives a telco voice saying "This number does not exist, please check the number and try again."
This behaviour is typical for first-stage automated robodialers cycling through a very large list of harvested target numbers (usually to create a shortlist of actively answering targets, before either onselling or using in the next stage of a scam campaign). Putting a fake Australian mobile number as the caller ID, instead of a blocked number, attracts less suspicion from targets and gives a higher call pickup rate.