I hired a contractor to remodel my house. He replaced a sturdy metal deck w/ a thin sheet metal one.My options

The contract stated: "The metal deck will be replaced with a metal deck of like quality" The original one was iron, sturdy and with checkerplate (non-skid surface). The one he installed is sheet metal, slick (risk of slip and fall!!!) and buckles when a 140 lb person stands on it. It is in no way of "like quality." I am refusing to pay the last installment of $4500. He insists that the deck is of "good quality" and he also said that another subcontractor put it in, not him. Your suggestions on what I might do now will be appreciated. Thanks!