please give me an advice

I got a freelance job to help a company setting up their database, I worked really hard days and nights and used my annual vacation to finish this project. The project was success completed, and I did not take their new project. by that time, they promised to pay me when I finished that project, but I just received part of pay. And they sent an email to tell me that they will pay me in a week. this was happened one and half month ago. now they did not reply my reminder email and did not send the check that they owe me. I don’t know what I should do, should i take legal action or something else? Please give me an advice.

I don’t have any contract with that company, only I have an email that they sent it to me to promise to pay me. Everyone think this can be evidence if I sue that company.