IIf your best friend says " I DONT BELIEVE YOU"..what will be your reaction??

I've never experienced ever hearing that from my friend, but me and my best friend had this huge misunderstanding once that she won't accept ANY explanation. It was frustrating, but all I could do was wait until she realized that I wouldn't do such a thing. n______n I did tell one of my friends I didn't believe her, she cried and said that I didn't know her that well to have the right to say that. After a few minutes of the confrontation, I found out that she really did spread the rumor ( so I was right not to believe her). She's one of the good two shoes type, the kind that people feel sorry for, and got the sympathy of most people. I didn't really care. At least I knew I was right. We made up already, but I don't think I'll ever forget that.

Definitely it will hurt me.But first i have to ask him/her why hes/her telling me that.Maybe there is a reason why hes/her telling me that.But if im telling him/her the truth and he/she dont belive me,well i cant force him/her.What will i do is i will prove to him/her that im telling truth and she/he must believe what im saying.In that case,maybe he/she can understand me and make some apology.And me as her/hes best friend im always accept her/hes apology.Best friends must be the best of friends.THank you...