Got sold a fake item, agreed to a refund, but where’s the refund??

Okay so basically I had bought a necklace marketed as a Vivienne Westwood necklace I thought it was a good deal so I bought it, later on that day the seller ships the item. I did ask if there was authentication as it specifically said it was authentic but the seller said there wasn’t any. I then saw the same necklace on Etsy so spoke to seller and requested a refund. On arrival I then receive the item and send it back. I don’t even open it. Seller then claims item got damaged in post. Ok. Whatever. But I have not received my refund, despite agreeing to it with the seller. I don’t have the item, nor the money I spent on it. And it’s been ages. Vinted staff haven’t really helped. Any ideas or tips?