You have proof of delivery, so will win an INR dispute.

The onus is on the buyer to provide the correct address for delivery. If it changes halfway through a transaction (or more likely they forgot to change it) then they wear the costs.

it seems the new occupant's of the buyer's old address have received the card and collected the item.

I wouldn't refund a cent, but I would suggest to the buyer that THEY contact the people at their old house and see if they can work something out.

It is not your problem.