If you paid for part of your order with a gift card, and the rest was on a credit or debit card, the full refund will be paid onto your credit or debit card.
If your whole order was paid with gift cards, the full amount will automatically be issued onto one of the cards. You can find out which gift card it was refunded to by checking the balance here.
If your gift card has since expired or you threw it away after completing the order, please get in touch with the team here.