Merchant not delivering the Furnitures as per agreed measurements&forcing me to pay remaining amount

The merchant is not delivering the furniture as per the agreed measurements and is forcing me to pay the remaining amount. He is asking me to visit his workshop  to convince me and get paid the remaining amount. So I kindly wish to know if I can get any advice on this situation. Can I take any advocate with me as a friend and check if they provided me with the correct furniture, and then only give me the remaining amount?