What can I do to get my money for an online transaction the internet retailer and the wire company refuse to pay

I was selling a computer on (company name omitted). Buyer transferred monies into my (name omitted) account, I called (name omitted) to see if the money was secure. They assured me it was, so I went ahead and shipped the computer. In transit, the buyer claimed his account was hacked into so (name omitted) took the ;money from my account and returned his money. He received my computer and signed for it thru UPS. What legal right do I have to retrieve my money. (name omitted) won't give me any answers. They told me to get a lawyer and closed the case. There are many other factors involved, too many to go into, I just need some guidance. I live in NY and shipped the computer to California.

Any help would be greatly appreciated.