A gentleman with an accent from the sub continent but a surprisingly anglo saxson name claimed to be an officer from the ATO. From the background noise and delay he was from an overseas call centre. I hung up on him.

They will call you telling you about a tax refund. They know your name. I wish I had a better plan for dealing with them, but when I asked them to read out my TFN, they said 'sure just one second' and hung up. Hope someone out there can be more creative.