29-06-2017 9:17 AM
Forget trading standards and government bodies. You are not a business seller so they don't apply and therefore he cannot have reported you - he's bluffing.
Your mistake was to refund immediately. You should have told the buyer to open a case in the resolution centre, and sent him a pre paid returns label to print. then refund through the case once you have the item back. If the tracking did not prove delivery back to you, you would not have been made to refund.
I'm afraid if you have refunded without following the correct procedure, you have given yourself a defect on your account, and there is no way to get the item returned.