I have an investment that I am having problems getting money out of. What are my recourses?

Since the sale of my house in California a friend of mine, who owns a Realty and Investment Company, has had my funds in an investment. As part of the deal "payable on demand" was included in the agreement. But for almost a whole year now getting money out of the investment has been difficult at best. At times I have missed paying bills, gone without prescriptions ect... waiting for promised money to arrive. I asked him to return the money in full once and he replied "4-6 months is the best I can do". Communications with him is getting harder and harder, phone calls go unreturned, emails go unanswered. Those funds are all I have. I'm disabled do to 4 heart attacks. HELLP!