I'll give that a go. It is frustrating because this is from so long ago. Could Adidas not contact me straight away if something was wrong?

I do have the tracking number but royal mails tracking website says unable to confirm the status right now. I think this might be due to how long its been because I do remember double checking the royal mail website after I made my return. Is there another way to find tracking information from August 2021?

The vendor was Adidas. I returned it using their label. Apparently it was refused by the recipient who wasn't Adidas and that it was retuned back to me. I actually sent them an email which, from reading the post you linked seems like a mistake. In it they said: The royal mail tracking information linked to your return further supports that adidas did not receive the return, as the parcel was refused by the recipient (which was not our Client), and returned to you as the sender. This is from so long ago so all I really know is that I sent it and that was that. The first letter was received in May 2022.

I have received a second letter from DWF regarding an order I made at a clothing store in august 2021. It says: “Whilst our Client processed the refund they never, in fact, received the products. The refund was, therefore, made as a result of a mistake.” They also said this: ”Ignoring this letter will lead to us seeking our Client's instructions to start court proceedings against you - making a claim for the recovery of a payment made under mistake - without further notice to you, and may increase your liability for costs. Further our Client would be entitled to claim interest on the amount refunded.” This order was from August 2021. They said the tracking information shows it was refused by the recipient who was not their client. I am told it was returned to me but I never received anything. This is from so long ago. Do I carry on ignoring the letters?