What should I do about a contractor I feel cheated me?

A few years ago I hired a building contractor that had a good reputation to build a 2-car garage. He gave me an estimate for $18,000. However, when he presented me with the bill, it was for $22,000. When I pointed out the discrepancy, he replied that the original estimate only included the labor and materials he used. Since he sub-contracted the installation of the electronic doors and the electric line to the garage, he had to add that to the bill. Not only that, but he only put siding on about 3/4 of the way to the ground. When I asked about that, he said that he would come back and finish it some other time since it required some masonry work he hadn't counted on. Months went by and he never came back. The particle board that isn't covered started to disintegrate and the siding that is there bulges out during warm weather. There are places in the lawn where the buried electric cable from the house to the garage is starting to stick up. Repeated calls to his answering service have gone unanswered. Have I been shafted again? What should I do?