Breach of Agreement

Hi I had accepted a outsource work(Translation) from a client. All the communications are done through emails.He made offer through email and i started working on it. No paper or online agreement is done between us. Terms are saying that 50% would be paid after translation done and balance 50% after 10 days. I received work in two batches. I received payment of 50% for first two batches and after 10 days when I asked client for balance payment he is denying saying my work is rejected by client. I asked him the reason for rejection and also offered him to make all the changes required free of cost. But he is not giving proper reasons and just saying my work is rejected. Now he is also threatening me to refund the money paid by him or he will proceed on me legally. In our communications or initial acceptance of offer, there is no mention of rejections or corrections till i asked him for balance payment. I need help on issues mentioned below. 1. How can i legally claim by balance amount from him? 2. Can he file a cheating case against me or can I file against him? 3. If he files a case, do i need to go over his place to defend my self(he is from another state)?