My Iphone 5 headphones is not working properly, problem with the cable, How to replace i got it from At

The connector in the iphone 5 headphones is not working properly. It works only when the wire near the connector end is held in a certain angle, when it is disturbed the volume goes very low (i think the wire inside is not proper and has some problems). I got the phone as soon as it launched in AT&T, where should i get it repaired or replaced, should i go to an Apple store or contact AT&T??. But i have a phillips headphones without a mic that works properly without any problems with the phone.