how can i sue someoene to give me the money back if there was no contract?

A lady rent me a room and before i moved she told me that i had to give a $800 deposit which was $400 for the month, and $400 the deposit. i was living there for 7-8 months and i never payed her late. i went to my parents house on april 2 because i gave birth and where i was staying i was by myself and i needed help. i payed her for that month because my stuff were in there. i also payed her for the month of may because i thought i was going back. i went back on may 8 and left may 10 because i noticed that place wasn't a good place to have my newborn baby. we spoke and we said in 2 weeks she was going to pay me at least $400 and in 2 more wee the other $400 because i didnt live the month of may. i have called her, went to the house and today 10/1/15 she doesnt answer the phone and havent payed me. what can i do?