Buyer demanded refund have proof item delivered

[fondian]

i sold an item recently and buyer basically bullied me into giving them a refund, accused me of not sending item on feedback and today i checked royal mail track and trace and found that the item was delivered today. Now i agree that it was slow on part of royal mail but buyer now has item that he essentially got for free. Is there anything i can do. I have both the receipt of postage and the track and trace from royal mail stating delivered