u/Few-Leave-8786

Returned an expensive item to a UK retailer almost 3 months ago, retailer denied having received it but tracking at time said delivered, I opened a case and just got a response from my card issuer today that claim is denied as retailer says I never opened a return and I have to give tracking details that show it was signed for to get a refund from them.

I don't know what has happened to the receipt, I normally put them in my drawer but can't find that one, it may of been thrown out by accident, maybe by my mum who loves to clean up when she visits.

I found the email with the QR code on it, how can I get the details from that? I assume I can't go to a Post Office and ask, and would feel weird even asking.