We are 95% finished with a job and things became contentious after we asked for 20k and the remaining upon finishing the job. Which amounted to aprox $3500 they gave is 10k then wrote a check for another 10k and canceled the check the next day. We said that was fine if we sever this relationship, you still need to pay us for the work completed minus the last few items on the job and you can find another contractor to finish. They do not believe that they have to pay for the work completed, only the finished product.
I am presuming the pay request was consistent with the terms of the contract. A contractor has the right to be paid for work that has been completed, accepted and approved. I would suggest you consult with an attorney to discuss the details, so the contract, project and payment history can be reviewed.