Assuming you have tried calling them several times and they have not been responsive, it may be time to consider legal action. The first step is to threaten to sue and report him to the Licensing Board in your state. The board will receive and handle different types of complaints such as fraud, deceit, gross negligence, repeated or persistent incompetence, or intentional misconduct. While the board will not have the legal authority to force a contractor to work, they may have the authority to revoke his license or impose probation. In some states, however, contractors may not be required to have a contractor's license, or they may not need a license for jobs which are under a specific amount. If the contractor you hired does not have a license, reporting him to the licensing board will nothing. In this can you could file a complaint with the Federal Trade Commission at www.ftc.gov and seek legal action by filing a law suit.
If you have a valid contract, you have performed your obligations, but the other party has failed to perform their contractual obligations, you may have the right to sue for breach of contract. The first step is to ensure you are within the statute of limitations for your state. State laws vary, but generally for breach of contract you will have anywhere between two to six years from the date of the breach to file your claim.
Step two is to assess the damages. If you have not suffered material damages from the breach, you do not have a case. For instance, if a painter has painted half of your house and the contract said it would be done December 30, but it is January 13 and it is not done, the delay and material damages from the delay may be considered minor. Review your states' laws for information about “material” damages. Damages must also be in the form of money (i.e. you have paid them $50,000 to complete work they have not done).
Some cases which are below a certain dollar figure (usually $3,000 to $7,500 depending on the state) may be settled in small claims court. Other alternative dispute resolutions such as mediation or arbitration may also be used. Contracts may also specify a certain remedy for dispute resolution.
Assuming you win your case either through mediation, arbitration or in court you will be entitled to compensation. The remedies for breach of contract can include damages (payments), specific performance, or cancellation and restitution. Restitution puts the breached party back to their original position.