Someone graciously informed me about a picture of mine that the same seller stole from me, and out of curiosity I looked through their store and found your image (and a few others, in addition to a whole bunch of official art they couldn't possibly have the rights to).
I reported mine to eBay, you need to report yours to eBay, too, so this person's items can be removed. They're making money off of others' work and our fan art! It needs to stop.
And to forewarn you! After being reported by several people for my Bumblebee Pikachu picture, this seller has tried just taking down the picture in an attempt to disprove that this is, in fact, MY PICTURE. I still have all the fanart T-shirts open, so if you need screenshots in the case the seller does this to you, too, just tell me.