Nothing you can do I'm afraid, if the seller is claiming there's a warranty be aware that only Australian registered authorised sellers/resellers of the product can offer warranties.

You are way out of time to do anything through eBay or Paypal

And, as mentioned, unless the seller was an authorised seller/re-seller of the brand, there never was a warranty to start with

You are covered by eBay’s MBG for 30 days from the delivery date. It’s to ensure that what you receive is as described upon delivery.

It’s not a product warranty.

In other words, there isn’t anything you can expect from eBay.

It’s too late for a chargeback.

It’s too late for PayPal Buyer Protection.

(In any case, these are also not product warranties.)

Is the seller - was the seller - an authorised Australian dealer for the headphones? If so, you should have some consumer protection. If not, forget it.