Brand sending legal threats

First – these products were purchased through an authorized distributor. abrand is sending me letters that I am not allowed to sell their products. I have received plenty of these types of letters. This one is different in the sense they have actually sent a server to my house to serve me a letter. Letter stakes I am not to sell their product, and even threatens legal action and “recourses that shall result in your ban from Amazon”

What validity is present here? In my experience, the brand should be contacting their distributors to cut off sales to online sellers. From the same supplier I have bought this brand from, other brands have set up that restriction from the distributor. The brand can also set up some sort of protection on Amazon, right? Am I protected by the Digital Millennium Copyright Act?

Again – I’ve received plenty of these letters and typically if a brand wants to restrict online sellers, they cut it off at the source (their distributors). No one has taken this many steps. Asidce from sending a server to my house, they have contacted me on my personal facebook, contacted a personal email (unassociated with my account), etc… I don’t even know how they have this information, but I’m ultimately wondering if I should be concerned, and what actions they can truly take.

Thank you