Stop - Exchanged product was not delivered

I ordered one long coat of Stop brand, but coat was one size bigger (L). So I placed exchange request. I wanted wanted that product at any cost because I liked that a lot. But SS didn't pay any heed of costumer's sentiments. And due to their slow procedure of exchange, the product went out of stock. They should have locked the product when they got exchange request.
I still want that coat keenly in M size.