Sued for an informal contract

I met someone through Facebook to take over the lease for a room of an apartment and he told me he would pay me $100 a month of the rent (1,200 for the year). We wrote a contract on a piece of paper and we both signed it saying they would pay me and by certain dates. I only received some of the money. They then went Mia and said they’ll pay me back but haven’t yet. Can I legally do anything about this?