What would you do in this situation??

okay, i have been friends with this girl names riley ever since like 2nd grade. we are in high school now. and shes not really the type who would believe all the hype and the rumors that constantly float about the school hallways.... but for some reason or another, this one girl has been messing with our friendship, and she, (her names hannah), has been telling riley that i've been talking about her.....i have tried and tried and tried and tried to tell riley that that is ridiculous and that i would NEVER do that to her....i mean, after all, she is my best friend, right?? whenever i try and tell her that thats not true, shes just so stubborn, and starts cussing at me, and telling me "what you did to me was beyond wrong..." and im just sittin here like, WHAT DID I DO TO YOU???? gahhh.....i just dont know what to do, any suggestions?