I signed a contract to rebuild my deck and repair the balcony. The contractor, at the closing of deck build, stopped the work and requests more money saying he had unforeseen costs or he won't finish the balcony repair. I paid him each installment based on the milestone of project and still has last payment left which is to be paid at completion of whole project. What recourses do I have if he refuse to do the balcony? Can I withhold the last payment?