Maybe the buyer is away and has not seen your emails.

Why are you involving Australia Post if you don't know if the item has been received yet?

You seem to be looking for trouble.

If the item does go missing the buyer has 30 days from the estimated delivery date to make a claim through ebay but 6 months through paypal.

Have you thought that by posting this thread you could be giving an unscrupulous buyer the idea of making a claim when they have received the item?  You have announced to the world that neither you nor Australia Post knows if it is lost, received or still in transit.