My home builder is threatening litigation?

I signed a contract that clearly states any changes made to allowances were to be approved and signed off by me. However, much to my panic, the home builder ran up a sum of $36K of overruns. I have consulted an attorney to make certain I was reading and interpreting this contract correctly and, according to him as well, the home builder failed to follow his own contract. Now the home builder is threatening litigation against me to collect. What organizations or agencies help people who have been wronged by their home builder? I already paid them $459K in full. The additional money they want for the overruns were things they added on their own without any consultation or approval by me. What happens if they sue me, too?