Bought vintage item in January, lost in post, Ebay didn't refund...

I bought a vintage and unique piece of jewellery in January. It got 'lost in the post', but it was unclear at the time whether it had ever gone out at all. Neither seller nor Ebay gave me a refund. It was more annoying than expensive. Seller has just relisted the same item for sale again. I sent him a message asking him to honour the sale in January. What else can I do please?