Neighbor is talking elderly seller out of selling his house. Sue?

We were supposed to close on Friday but had to extend the date because it was determined that the house is in pre-foreclosure. Then, we get a call from the seller’s neighbor telling us the seller doesn’t want to sell the house, that it shouldn’t have been listed, that the seller is an alcoholic and can’t remember selling the place. He had us on speakerphone and the seller was there with the neighbor. He has signed the purchase agreement and just signed the extension on Friday. We already wired the money! What can we do about this neighbor interfering like this? He may be the sole cause of this falling through. He’s a commercial real estate agent and acted on the phone as if we would never be able to enforce the sale. He said he will claim that the seller is incompetent.