Neither, unless the is registered in Australia AND an authorised or reseller of the product
Otherwise, the word warranty is nothing more than a word on the screen
eBay do not enforce 'warranties' at in point in time
Your messages need to be kept within eBay messages, not via email
(Personally, I would not be responding to eBay buyers if they were sending messages to my personal email
either)
If you did indeed contact them via eBay message and they did not respond. most likely it is because they are not an authorised seller of the item, ergo cannot provide the 'warranty'
IF they are an authorised seller, try contacting the company
