What can be done if a contractor doesn't complete the job?

Our contractor has several things to complete on the job he was hired to do. He was to complete it in 6 weeks and after 6 weeks it wasn't completed and he took another job. He came back once and did some work but it still wasn't complete. Should we offer him more money to come back and complete the work? Can a court force him to complete the work as we foolishly already paid him? We have the contract with the items to be completed. We cannot get a response from him on when and if he is going to return.