Sent incorrect product

I bought an item from Buyfast. It arrived in good time but was the wrong product (red and not wooden). I called and pointed out that it is the wrong product (the blue one has another product code), but the customer care staff member stated that they cannot exchange if product was bought with a voucher and that exchange will mess up stock controls. I was referred to customer care manager (Jay) who stated the same thing. I maintained that this is not an \exchange\", but that they sent me the wrong product. We then looked at the catalogue online and Jay agreed that the product I ordered was not sent to me. He said he will get back to me. I have heard nothing since."