How do I pursue a buyer for non-performance?

I have a contract to sell a home located in NY. There are no contingencies. We were supposed to close in November but found out in October that the well is on the neighbor's property by 3 feet. Neighbor is willing to do an easement which has been drawn up & sent to the buyer and revised to meet their wishes but it's still not agreed upon by the buyer. We are nearly 30 days past the closing date now. What are my rights under this contract to hold the buyer accountable for closing?