He might have thought you’d given up on it. Still, would have been nice of him to get in touch with you to find out what was happening. Did you have an exclusive license to convert the Wordpress theme… i.e. was there anything in the agreement that stated he would not sell the rights to anybody else?
Either way, I’d get in touch with the author and see what’s happening. You can drop a line to support if you like, but it’s unlikely they’d get involved. If he has an agreement with the original author, then he’s not done anything wrong in the eyes of Envato. Well, I guess that does depend on the content of the agreement, but still… the issue really lies between you, the original author and the new author.