Contract signed title clear now it's a problem

[Donald Powell]

I got a contract for a house signed. Sent info to title company, it's clear. Found a buyer, he signed my assignment of contract. When I call the seller to give close date, I'm told I have to talk to someone else, Her brother. Once I talked to him, he told me the house isn't for sale to you. He just put it for sale with someone else. My contracts are legal. The are elderly. How do I approach this. Or just let it ago?