REFUND DENIED

I had purchased 4 trousers from H&M. Due to fitting and colour issues, I returned all 4 trousers. The delivery agent who came to collect the return checked the items and packed them himself. After this, H&M denied my refund for the returned trousers, claiming that the items received were not the same ones I had purchased. I asked them to send the trousers back to me so that I could file a complaint with proof, but they refused, stating that they no longer have the items with them. I got refund of 1 and seeking a full refund for the 3 trousers that were returned and collected by their own delivery agent.