First of all you say the buyer has confirmed he has received the jacket,
So you are covered. You are also covered since you have posted the item, the proof of delivery is fine, even without a signature showing since it will show his address & postcode on the royal mail/post office receipt.
You have all your correspondence which you can use as evidence against the buyer.
The fact that he has confirmed receipt and now has filed a charge back for the item IS FRAUD. Supply the card company & paypal ( since the chargeback will have a case open in paypal) with all the tracking and correspondence information.
I am glad ebay chose in your favour with the SNAD case, that doesn't happen to often. 
What is the reason he wants a refund and refuses to return the item to you?
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