Informing Amazon About A Seller

How can I inform Amazon that one of it's sellers is not being truthful with customers about a product that is being sol?. I ordered an expensive office chair - the website said in two places on the order page that it was a new chair, just open box. I wrote to them prior to ordering asking specific questions about their open box products. The response was that this was a new chair and that open box meant they opened the box to examine for damage only. I received the chair and it is definitely a used chair. The seller wrote me and said ooops sorry we made a mistake and sent a used chair but we don't have any new chairs in stock. Now I notice on Amazon that the seller has changed the order page and left off the new and open box info. However, they now have another page with the same chair at $200 more. When I ordered their were four chairs listed, now there are only three and the two pages are identical listing three chairs available except for the difference in price. I don't believe Amazon monitors the correspondence between buyer and seller and they need to know what this seller is trying to do. When the company wrote me they offered to give me a partial refund if I kept the chair. I truly believe this is some sort of ruse to just sell used equipment to unsuspecting customers. I also believe that have new chairs in stock they are just trying to make it appear as though that is not the case because of my complaint.