Failed Delivery-advice please

Hi, I have been contacted by a buyer who is looking for an item purchased on 22nd August. I have managed to track the item via the recorded delivery receipt and it says an attempt was made to deliver on 27th but package is being sent back to sender as recipient 'did not pick item up or we could not deliver the package' Given the time scale it doesn't look like the PO kept ahold of the package for any length of time to enable them to pick up. I can't find out how long they are supposed to keep it.Given that the buyer is chasing the item I presume they were not left a card by the PO. So who is responsible for postage costs if redelivery is requested by the buyer?Thank you.

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Orignal From: Failed Delivery-advice please