Contractor wont finish the job he started, what should my next step be?

I hired a contractor back in January to replace one side of my roof that leaks, replace gutters, put down insulation, paint three rooms, and put up a drywall ceiling. I paid him 3/4th of the money up front, we agreed he would get the rest when the job was done. He did all the painting and the drywall, and bought the insulation, last time he worked on the house was the first week in February. The painting in spots is blotchy, called a few times to ask when he was coming back, every time he acted like we were bothering him. Finally he said he was coming to work on the roof, but he needed the rest of the money, we told him that wasn't the agreement, He then started to ignore our phone calls and texts. We finally got him over to talk about the job and said he will take half of the rest of the money before he starts work again. We told him no and began questioning why this is dragging on for so long, he got upset and ran out and said he would call us Thursday. This was two Thursdays ago, and we ha vent heard from him. What should I do now, how do I get the money back for the work that wasn't done??