Its a constant daily battle.
I send the seller a message like below. Quite a few message back and say they will remove themselves but normally take a while to do it.
I see that you are selling xxxxxx on Amazon. However, I have created the xxxx brand from scratch, and have never resold any wholesale items to any other reseller.
I own the brand, and have not authorized you to sell xxxx products on Amazon.
If you are selling a different brand, while posturing as xxxx, then you are selling counterfeit products, which is something that Amazon takes very seriously and will shut down your account without warning.
If you do not remove your product from our listing ASIN xxxx immediately, I will have to contact Amazon and issue a formal Cease and Desist letter. This is obviously not an ideal situation for either of us, so I hope that you take heed to this note and remove your product from our listing.
Thank you for your prompt attention.
Your name and company