My house passed the city's final inspection on March 10 and I moved in. However, I found that the air conditioner could not work. I asked my contractor send someone to check, but he refused to work, and asked me to complete the final payment $2700 then come to work. I did not agree. On June 25, the contractor sent me a line saying that I did not pay the extra work, $150,000. And required to pay 12% interest. He had not made this request before. We pay for each additional work after negotiation. He only wrote no specific items for the amount. Is this fraud? And obviously this order has been more than 90 days, is it effective? What should I do?