I think the 3 months was PayPal now 6 months, not Ebay, did you pay with PayPal if so open a case with them.
I always thought the 30 day period for returns on eBay was from date item was received not shipped, but that is for when the seller offers 30 day returns and you received the item, not for eBay money back guarantee.
What does the tracking actually show on your end in the USPS system not the screenshot seller provided.
It is 30 days from the estimated arrival date for an item not received
https://www.ebay.com/help/policies/ebay-money-back-guarantee-policy/ebay-money-back-guarantee-policy?id=4210#delivery-dates