You really need to review the contract terms or have an attorney review the contract terms to see if there are any "loop holes" to allow you to terminate the contract early, or ther have been any breaches of the contract by the broker to allow early termination.  A judge would look at that contract as binding between you and abide by the terms.  They would assume that you read it, negotiated the issues and signed it freely.  If you agreed that they would receive half of the commission if sold during the term by you or others then you could be bound by it.  You did not state what the rateof commission is but you agreed to that as well.  Please seek legal help.  Good luck.