Denial of Payment

I am a 4th year college student. To earn some money for personal expenses I do some freelance work building websites. On the 1st of Nov, I was contacted by a past employer, Rishav Goyal and he pleaded me to take up a new job he had for me. He said that I would be payed 7-8k for it. This past employer is an alumnus of my college. He had posted the same job on the college mailing list earlier but had not gotten any response. Since he was an alumnus and was really pleading, I agreed to take this job up. But the requirements document that was provided was very vague and poorly drafted. I had immediately contacted him with several doubts, some of which he clarified by the 3rd of Nov. So I made the website according to his specifications and gave him the code by the 5th of Nov. He then tells me that the website was for his uncle and the uncle would like a demo. When I give the demo to the uncle, he gives me different specifications than those mentioned in document the and asks me to redo the site. After looking at the new requirements, I contacted Rishav and told him that the work has increased and that we need to renegotiate the price to 10k. He discussed with his uncle and told me to go ahead with the job. So I make the changes and turn in the code by 12th Nov and tell them to contact me with changes by the 16th of Nov, since my exams will soon start. They call me on the 21st with new changes. I tell them that I my exams are going on and I can give them the changes by 1st Dec, to which they do not object. I deliver on the 1st Dec as promised and contact them for my payment. They avoid me for 10 days and finally on 11 Dec, the uncle calls me to tell me that he no longer needs the site and he won't pay. He states the reason as: "I have taken 2 MONTHS to do the job and he no longer needs the site". On contacting Rishav, he tells me that he was only the guy who introduced the 2 parties and is not responsible for the actions of his uncle. I have emails and facebook messages to prove all of above. What can I do in this situation? Please help me.