nightmare renovation

need some advice I contracted a design firm for gut reno of a 1-bdrm coop. part of the renovation was to convert to a 2-bdrm. the architects came up with an innovative design to create a second bedroom w/o losing living/dining rooms. work began apr 2013 and was estimated to take 3-months. after the work was completed, they failed to close off the second bdrm (nursery), so now there is a 1-ft gap btwn the end of wall/window leaving the nursery open to the dining room. I'm trying to have the work finished amicably, but it's been months of empty promises and am wondering what I should do at this point. Should I get lawyer involved ?