Sould I send my ex a letter?

I would have to agree with Professor Logical. For a girl to say something like "I'm just not ready yet" is typically an indicator that she wants to break up, but doesn't want to hurt your feelings. The fact that she hung up on your calls is another pointer. Since you already bought the bracelet, I would go ahead and send it to her with a note that indicates that its from you. I wouldn't, however, get your hopes up.