Sony - warranty problem

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My Sony Xperia S tablet is less than three months old. This is the main cable connector which has come apart. Sony are refusing to replace it under the warranty because it is 'broken'! Why shouldn't the warranty cover something that has failed so soon after purchase? Surely there must be some kind of manufacturing failure if it comes apart so easily? Sony want me to pay £34.66 for a replacement! and of course the only place I can buy a replacement is from Sony. Sadly when I bought the machine I thought Sony were a good company that I could rely on - seems I was very much mistaken :(