All of your answers are in your contract. In Arizona, we have a "cure period." This is the time frame in which the Buyers have to "cure" their breech of the contract. Your contract is your legal leg to stand on. Do you have a good working relationship with your REALTOR? Remember he/she is on your side! They want to close this deal as well. I understand your frustration. Keep the dialogue open with your agent. Try to remain calm, as this is a very emotionally draining process. If need be, have your agent get their Broker involved. There are many ways to close this transaction gracefully. It all starts with communication, and your contract. Best Wishes for a successful closing.
The termination process should be outlined in your contract - earnest money disposition, etc. etc.
I empathize with you after having been a seller as well as a listing agent in Georgia under similar situations. I think Nancy's answer and recommendations are well worth considering. If the listing agent or broker cannot break the log-jam (so to speak), then seriously consider seeking professional legal counsel from a good real estate attorney.
Wishing you a swift & successful outcome. - Ted Shoop