Brooklyn, NY based law firm failed to file USCIS immigration documents., employee stole money orders now firm delays settlement, blames employee.

In 2011 I hired a New York City based immigration law firm to handle the migration of my foreign based family to the United States. I am a US citizen. I was led to believe that documents were filed with the USCIS and I need to wait. I trusted this firm because I had successfully done business with them before. I continued paying their legal fees, and applicable USCIS money orders to the said law firm for transmission to the USCIS. In 2014 after my own investigation with the USCIS and State Department I found out that not a single document was filed. An employee of the firm was fired for fraud not only against me but other clients. Since then I have been negotiating with the firm for compensation. I had an oral agreement with the head of the firm for a settlement which he reneged upon. Eventually earlier this year the firm decided to settle and I signed a release agreement. The firm has now apparently reneged on that agreement. Can i sue?