Probably reason for delay was that your answer was all wrong. Buyer should have opened a NOT AS DES CRIBED CASE, YOU provide return label and refund on return.
If buyer has just returned without opening a proper case, then they have spent money on postage, which should have been your responsibility, and will have no means of enforcing s refund as ebsy will not have been involved.
You say they have sent a return via ebay, I do not know what you mean, but if ebay are involved then you may get a defect, and ebay refunds at your expense, when tracking shows as delivered.