Mailing back to the UK is actually simple and rather cheap. I have mailed stuff back to Wiggle, but not PBK. Less than $10 is you pack it tight in a very small container like the priority mail boxes or envelopes. I would not let the shipping be the one thing from keeping you from returning them. Contact PBK FIRST and ask about their return policy and procedures.
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Arguing with ignorant people is an exercise in futility. They will bring you down to their level and once there they will beat you with their overwhelming experience.