Im so confused, how is it that other sellers are able to sell on my own brand registered listing?

Is this really a thing? Random sellers can just sell on my listing anytime they want?

Someone sold on my listing for a full day, and I ended up buying the rest of their stock just to get them to leave the listing, and I got the package today and its all counterfeit, now im going to get tons of bad messages on my legitimate listing that the product doesn’t work.

How do I stop this??? How can I make it that only I can sell on it??

Did they fake some brand authorization documents or something, or can anyone really sell on anyone’s listing anytime they want?

And now I can’t even report their listing because they are no longer selling on it.