I bought a pair of Apple in ear headphones from eBay. It was supposed to be knew, but was open boxed. Anyways, the left earbud has really low/unacceptable volume. Even when I fully blast my iPod I can barely hear it. I've tried putting in the right earbud in my left ear and that worked fine, and I tried it on another iPod and my Mac. So it's not my ear, it's the earbud. Anyways, every # I try on the box is not accepted in Apple's support. "We're sorry, that serial number is invalid". What should I do???