Well it could be 'ambiguous genitalia', I've seen does that looked like bucks or bucks that looked like does. Also bucks can pull their testicles inside their bodies, had a buck that often appeared to only have one, tap on him and he suddenly had two. Seen it happen at shows too, DQ for one teste, rabbit comes off the table and he's got two visible. Size bothers me, at eight months he should be bigger, sounds stunted, or younger than she initially told you. I've had rabbits from large litters be smaller and slower growing because I didn't cull kits and let them all live, and I've had just plain old runts stay small for whatever reason. That could be your situation. Doesn't sound like your going to get far with the breeder, it is for the most part a buyer beware situation in the rabbit world, thats why I always have someone esle check out buns before I buy them, in case they catch something that I miss. You've also had him two months, bought him at 6 months, his testicles should have been visible then. I myself wouldn't refund or replace a rabbit that had been out of my hands for 2 months, but then I would have sold him with a clear conscience, or not sold him at all. Sorry your in such a bummer of a situation, hope it wasn't an expensive lesson.