How can i unglitch my pokemon white game?

Alright,Ii was at the Pokemon League. I beat all the people before the the champion, went to his "castle" and met N then went into N's castle, caught Zikrom, beat N. and was challenged by Ghetis, lost to him, and then i got more supplies for battling Ghetis and now i can't get back into the pokemon league or even talk to Ghetis. Is there something i can do? My friends say i glitched my game but i have a hard time believing you can glitch it that easily.