Blocking a buyer from buying my product

So i manufacture a product that has sold very well on ebay, then of course a Chinese seller saw that my product was selling well and bought and copied it. And now this is happening here on amazon. I’ve searched the shipping address and can tell its a chinese company who is going to copy my product. I tried to block it, when they purchased first i cancelled it and said it was out of stock. Then i set the stock of the product to 0 for a few days. then once i updated the inventory the same user bought it immediately . Not sure what to do at this point, just cancel it again and not be able to sell it on amazon, or let them buy it and try to compete