Haha, same here. Not much I can do about it though. I left them a message on their youtube profile page comments, but I doubt anything will change. At the end of the day, it's free promotion, which I don't have a problem with.
Well, they DID link to your Deviantart account in the description, which no one will read as they continue to rant about a movie that won't be out for three years being about alicorns in an image even older than Season 3, all because your art is way too good.