Sorry to hear about your situation. One would want to review the agreement, seeing whether it states that it is the entire agreement. Generally speaking, the written agreement will control. Best to consult with an attorney to review the contract and discuss with you the facts in more detail. Avvo has a great "Find a Lawyer" feature to find an attorney. Best of luck.
Answer given for general advice and is not a legal opinion, which would require an analysis of the facts and circumstances as well as the applicable law and regulations.