Hi,
You need to check with the seller to see if the VAT collected at the time of sale was sales VAT by Australian authorities?
If so then you need to raise it with them. Anything posted or couriered to you from another country goes through customs to check it is not banned or restricted and you pay the right tax and ‘duty’ on it.
More information is on below link:
Tax and customs for goods sent from abroad
Thank you.