Seller has accused me of copyright infringement

Help - another seller has accused me of copyright infringement. They are claiming I’ve copied their product description text. Is it even possible to copyright your own Amazon description text?

My product is unique, I own my own brand. I can see the seller sells a similar product and we do have the same Amazon description text - I can only conclude they have copied my text as I wrote the description text myself.

I’ve appealed to Amazon and they have written back saying I need to provide a letter of authorization (LOA) or licensing agreement (LA) from the rights owner indicating that you are authorized to use their intellectual property.

I’m completely shocked and don’t know what to do.