It is indeed the ATO - the Advance Collections Department. I'd still suggest you call back on the ATO's advertised number and explain the 'phone call, and they'll put you through to the right department.

The reason they call other people (rather than you) is because their records may be out of whack (regarding your current address & 'phone number), and they have somewhere on their system the other person as being connected with you.

This is a tax office number. If you get a message to call this number is 1300 880 217, its the early collections area of the tax office. And they mean business if you have debt with them.

They are definitely the ATO. I rang the ATO's own 13 11 42 number as published on their website, and they gave me this number as their "early collections" department. I specifically asked if it was an external agency or the ATO, and they said it was the ATO.
Not worth your while to avoid... talk to them and make a payment arrangement!

I had a missed call from this number so I rang them back which was the ato number, was talking to the lady she told me there was no notes on my file about being called or needed to be contacted so she said to disregard the message.

They are the ATO. Fail to communicate with them and you may end up having your bank accounts garnisheed.

Introduced himself as ATO but seemed suspicious. i.e couldn't pronounce the word proprietary ?!

They're a collection agency, mostly deal with peoples income tax accounts. They're part of the ATO however they're a different department.

Stated he was from Tax Office. Left message on my mobile, Asked for Tax File Number. My accountant said not to call back and give it. Seems dodgy.

Introduce themselves as the ATO, they are not.

Its the ATO