The same things happened to me...that headphones broke and so did the USB. I just popped in and they helped me. They said that you are not supposed to do the instore exchange of the headphones, but they did it anyway. They said you are supposed to call apple at 1-800-APPL-CARE and they will take care of it...With the USB, they put up a fuss. They said that it was my problem that the cord broke and that they would not exchange it. After a few minutes of going back and forth, they finally gave in and said that they would do this as a one time exception. I had to go to the extreme of calling Apple's quality poor
That's just my experience with changing the headphones and the USB.