No, there are no refunds, it always states that on the right side of screen, when you go to purchase it, read description of dlc, you'll find that message in().
As for the $ error, I wouldn't know about that, since I can no longer buy dlc... and it's not just me. You see there is an invisible wall that won't let you go past 14/15 dlc packs or else you'll get your game data corrupted(so far the only remedy to fix this problem is to delete saved game and dlc just bought(with no refund); this is a friendly warning from one of many who have had this happen to them, and so far Koei hasn't done anything about it and it has been about month now since this became an issue, with no patch in sight.
You don't need to delete your save if you encounter that error >.>
Just delete some of the DLCs you're not using. I recommend stage packs: how many times are you *REALLY* going to play the same three stages? How often are you actually going to use an animal other than Red Hare or the harrier?