This unfortunately does happen, and there's nothing that eBay can do to enforce the buyer to repay you.
It has just been a long weekend holiday they may not have seen your messages, or they simply may not know how to repay you, as this cannot be done now through eBay.
Wait another day if they do not reply, send a polite message to say you do apologise for the long delay to their item, but you can see now and have the tracking to show, the item has arrived please can they repay you this way.
They can pay by cheque, bank transfer or a PayPal Friends and Family payment, or you can send them a PayPal invoice.
Nothing to enforce them to pay, but most people are honest and once explained how to repay, you may hopefully, find payment's on its way.
@jayscorch
