Returned the missed call (with my caller id blocked) and message "Optus advises that the mobile number you have called is disconnected" even though I called a landline. Suspicious, unsolicited telemarketing from a call centre or possible scam? Either way - don't answer it.

Didn't answer it - tried calling it back - saying call could not be connected. Similar Prefix and close suffix range for other numbers reported as spam - so blocked and reported as Spam with Apple (not that it makes a difference - especially with Apple)