Must I pay a company for the balance of a job if the it was not completed in a 'reasonable and customary' timeframe?

At the 2 year mark, I filed a complaint with the BBB against a local window company and CC'd the company. It was a 4 page recap of all the problems and issues that occurred along with a list of final demands to get the job done including a 'final payment of $500 in installments'. They completed the list in 3 1/2 months. They had to renew the permit to finish it. I gave the company $6500 up front. Issues such as a severely injured worked who sliced his hand with a blade on day one to wrong sized windows to torn screens to a window that did not function and was that way for 2 years to improperly functioning locks and more. Communication was poor to none between the company their contractors and me. They say they will call but never would. Not showing up when they promised, etc. I have now missed the time frame for a rebate through the government. There are many complaints against them online. Must I pay them the remaining $6,000? Please advise me.