There is no way to get around your problem. eBay only cares to keep buyers happy and has little to no concern about wether you are right or not. You are better to agree to have the item returned and have something rather than nothing. If you sent the item registered and insured you might be able to lodge a claim with Australia Post all though technically the person recieving the package should be the one doing so. eBay is no longer a real Auction Site as it once was, it is now simply a huge Mall where they reap the benefits from sellers through listing fees, selling fees and from store front fees. Honest sellers take all the risks and when things go wrong like in your case 99% of the time eBay will find in favour of the buyer no matter what proof or argument is put forward. I've been down this path many times and each time I get the same emails with the exact same wording so don't feel bad, you are not alone in discovering you mean nothing to this behemoth we have all helped to create and happily keep on feeding.

Cheers