This is the usual advice, pick it up from whatever position your order is at -
You need to be extremely careful how you handle this as you could be seriously out of pocket if you try to handle this yourself.
Your buyer needs to open a case for not received and you respond with the tracking number proving delivery to the UK Global shipping hub – you should have actually put the tracking in to the transaction at the time of posting.
You cite that according to Global T&C you, the seller, are not responsible for any loss or damage in transit once it has arrived at the Global hub.