Buyer “Refused to accept delivery”

Hello. I recently sold a computer part worth ~£600 on eBay which was sold yesterday and dispatched with Royal Mail Special Delivery. I’ve just looked at the tracking and it says the recipient refused to accept it and is now being returned to me, apparently today.

There is no message from the buyer, but I’ve just messaged them asking what is going on.

Looking at other posts, i am aware that they waive their protection when they refuse an item. But in the case it was a mistake, (he sent it to some corner shop? - this was confirmed to be the correct place as I messaged him before I paid for the label) how would I be able to get the money for re-postage, and how would I change the tracking number? If they end up not wanting it back, am I able to only refund the price of it, taking away postage and a restocking fee? Thanks