Depends on your contract--review the document as the answer will more than like be in there--or consult with an attorney who specializes in real estate, have all documentation reviewed and see exactly what options you may have and then go from there--most professionals do offer a free consultation.
You will need to make sure the contract was in writing and signed by both parties. you will have to show what they breached and have proof of it. Your best bet is to meet with a real estate attorney for at least the first free meeting and get some direction. Make sure you keep all your records and write down a timeline of what happended. good luck working things out