It seems clear that she has moved on and doesn't want to talk to you. She probably got involved with some other guy. Or maybe her brother told her to end the relationship. I understand that you want to find out what happened and at least get some closure, but she clearly doesn't want to talk to you. Just move on. If this is how she handles situations, you were never going to be happy with her in the long run. You deserve better than this.
Good decisions come from experience. Experience comes from bad decisions.