Not too much you can do 3 years later. It should have been disputed when he filed the claim. You should have shown PayPal the tracking number for the item sent and kept up with all emails and shown them to PayPal & eBay. I got burnt once back in 06 and I learned my lesson.
I always keep up with all messages and emails and tracking numbers and I always get confirmation delivery. I take a picture of it and show it to the buyer so they also have the exact tracking number. Even with members on here, I do the same thing. Even if I'm giving them something just for the cost of shipping, I still show them a pic of the receipt and confirmation delivery tag.
Anyway, three years later, you're a bit too late to even bring this back up. If he says he emailed you, you should have responded. You must not have because you would have known you had a file claimed against you. PayPal emails you too so they can hear your side of the story. Apparently, you didn't answer.