"Optus regrets that this number has been disconnected"
In other words: SCAM Call

Caller: Australian Cybersecurity [Something]

I believe it was a scam. Sounded very dodgy. When I rang back the next day there was very embiguous voicemail message. Gald i'd hung up.

So annoying. Woman asking about my paypal account and authorising a payment for 900 dollars - scam call. Pretended to be some security company but you can hear other calls happening in the background. Indian accent - I drew it out a bit to see where it was going but they hung up fairly quickly.