The buyer should have received a QR code that should have been scanned when the item was picked up. If his grandfather picked up the speakers, he should have signed and added that he was picking up the item for his grandson.
Communication should always happen on eBay. Do you mean SMSs with texts? Another seller had a similar problem recently. If the buyer had confirmed receipt of the item in an eBay message, maybe you would have had a chance, but now it is difficult, judging from what other sellers who were scammed in a similar way said on this board.
