I have bought the game from the store and in the store they said "no refunding". I played it and noticed, that they never gain exp, I have ony gave them potions and berries, but no exp. What should I do?
I've heard about this problem. It's basically to stop pirated copies from selling, or people ROMing them (though ROMs have a patch to sort this problem out). So here are a few things that might help:
By the way, if it's #2, then there's no way to solve that apart from getting a new DS or a DS Lite, or copy of Black 2 that's the same region as your DS.