How do i sue a business?

I hired a company in Brooklyn for my kitchen cabinets. The designer that took measurements made many mistakes. Cabinets came in wrong sizes, even though my contractor made clear of what he wanted. The installer negligence cost me an additional 7,000.00. He forgot to put a 2" insert on each side of where the stove needs to be. The granite was cut but because the inserts were not put in place, the countertop was short 2' on each side. I've filed a complaint with BBB. Please let me know what else i can do.