Never allow a seller to string you along until the Paypal filing deadline has past.
Never allow a seller to make your refund contingent upon leaving feedback!
All you had to do was file with Paypal,return with the required delivery confirmation to the seller.
Paypal would have decided in your favor and issed a full refund.
Now your seller has your money, the item back and a positive feedback
Why do buyers allow sellers to bully them like this, when Ebay/Paypal gives buyers the tools to quickly remedy this kind of situation?
Did you fund your Paypal payment with a credit card? If yes , then file a chargeback with your card issuer now.
If not, then there is nothing you can do,except learn to follow Ebay/Paypal policies, when the item is not as described.