How can I get paid for the money that is outstanding on a Housing Authority project as a subcontractor by unwilling GC??

I worked on a project for a GC with a subcontract agreement to subtract actual payroll costs from the subcontract during the progress of the work. The GC wrote in the subcontract that I would be compensated the remaining delta. They provided the materials. I provided the field sampling and laboratory testing via 3rd Party. The GC is unwilling to submit a significant change order for the benefit of the subcontractor due to his relationship with the owner. The outstanding change orders for unforeseen conditions, winter concrete protection, and filling voids in substrate exceed $50,000. The remaining balance of the subcontract also exceeds $50,000. Please advise.