How do I start the process of getting paid for a job that was completed 10/2019?

A general contractor contacted us to finish a job after a contractor was removed from the job. Our company was on site from 8/2019-10/2019. We received payment one on 9/24 for august. We signed a conditional waiver for payment 2 on 12/20, for $25k. We received half of the 25 on 12/27. They are refusing to pay us until we sign a unconditional waiver. We refuse to sign it because a vendor listed on a schedule value did not get paid since they didn’t pay the whole amount. The vendor has now put a lien on the general contractor for non payment and we are in grid lock, the general refuses to pay the vendor until the waiver is signed.