Symbio Networks are providing safe haven to scammers. Over 90% of those scam calls (Fake ATO,Centrelink and tech support) come through an Australian VoIP number provided by Symbio Networks. The scammers use these Australian VoIP numbers provided by Symbio Networks to help give the perception that they are in Australia. Symbio Networks don't do anything to prevent this and they refuse to remove these numbers when I report them.
Looks like a reverse-charge scam, called twice and left a voice message (with Australian accent!) saying 'Hello can you hear me'. The number appears to be Melbourne but has an international code. Don't call back!!