Is it a scam?

Story: You get a phone call. The caller says they’re from the ATO. They want you to pay a debt (which you know nothing about), or are asking for your personal details.
But it doesn’t seem quite right. Maybe the caller:
is aggressive threatens that if you don’t pay you will be arrested and sent to jail, or
tries to make you call another number outside normal business hours.
Or maybe you have received an email or SMS offering you a tax refund or asking for personal details, but it just smells wrong.
What to do if you think it is a scam?
You need to check it out.
If you get a phone call, ask the caller for:
their full name and extension number
their team leader’s full name and extension number.
You can call Etax Plus on 1300 221 125 or call ATO on 1800 008 540 to verify that the caller is from the ATO.
If you receive an email or SMS, do not open any attachments or hyperlinks. You can report the email by forwarding the whole email to ATO at Report email fraud. You should then delete the email or SMS. You can also call ATO on 1800 008 540 to report the email or SMS.

Source: ATO