Will law help me recover my money from pool contractor, need my money back!!

I had a written contract to build a pool by contractor and he took 24 K advance to do the work. After 3 wks of no work he returns with another contract of almost 1.5 times the original amount saying the work cost more than he thought and wanted us to sign new contract. We refused to sign and wanted our money refunded. We also put a legal notice of 30 days to refund our money. He doesnt want to return my full money ( wants to keep $8500 to his pocket with 0 work, just giving bids and holding my money and work for a month). What should I do, I want my full money refunded??? Can law help me to recover full money?