Shein Return Rejected - Refund Issue

I recently placed an order with Shein for two identical tops, “Olive Green Pleated Square Neck Plus Size Women Long Flared Sleeve T‑Shirt.” I accidentally ordered two pieces instead of one, so I decided to return one of them. I sent the return around Monday, 2 March from Huércal‑Overa, Spain, and the order reference I have from Shein is GSO15S15500NWVY. Now I have received an email from Shein stating that the item I returned does not match the returned item, which I do not understand at all. Both tops were exactly the same, and there were two sachets with the same item inside. I suspect there may have been a mix‑up or confusion on Shein’s side with the codes or labels of the items. I request that Shein recheck my return, correct this apparent error, accept the returned top and issue the appropriate refund for it. I would also like a clear explanation of how this mismatch was determined, as I am certain that I returned the correct item.