Mercari complaint: Seller swapped a gold necklace for fake jewelry

Ok so I’ve been a long time seller on mercari and have amazing ratings..over 230 actually ! A buyer ,name aria pezeshki who lives in ca.purchased a men’s 10k solid gold mariner link necklace..22 inches ..that weighed and appropriate 22 grams, once she received my item.she made a claim.to mercari saying my item wasn’t as described which mercari then approve her return request! That was totally fine,however once I received my package back it was definitely not a men’s gold necklace, actually it was a ladies 9inch silver tone anklet ,basically costume jewelry that has no worth .I’m literally heartbroken that someone can be so cruel! And evil with zero remorse @ i contacted mercaro after they asked me to hit and to accept my delivery which I gave them detail of that had taken place. Which mercari rudely said they canceled the transaction and refunded the buyer since they couldn’t prove she sent that costume piece of jewelry back ! I have proof because the weight of the envelope has to be much lighter in weight of course ..mercari didn’t offer me a credit orn nothing.. no type of resolution