your buyer need to send you a feedback revision request.
however you have a much more serious problem now that eBay are forwarding details to HMRC.
You are a business seller trading as a private seller in violation of eBay rules and the law.
you cannot refuse returns as your listings state - "No returns accepted", also you claim further protection by your improper registration - "Consumer protection regulations resulting from EU consumer law are therefore not applicable. eBay buyer protection still applies to most purchases."