Amazon is a marketplace, not a retailer.

They are not selling the knock off, they are allowing the knock off merchant to use their marketplace.

Your remedies are with (assuming US based):

* Copyright enforcement via DMCA on your marketing info/photos etc

* Trademark enforcement via Customs and USPTO

* Design patent enforcement via Customs and USPTO

It's not Amazon here that is the issue, it's enforcement by the governmental authorities that are supposed to do that enforcement.

You'd have exactly the same problems if you were selling on etsy instead of amazon, or at a local weekend handicraft market.