I rented a room from main tenants(a boy and a girl)

before paying the deposit, they told me the whole unit can stay 7 ppl. But after moving, they told me they made mistake that the whole unit can stay 6 ppl only(i am the 7th). So that they can not register me to the landlord. Besides they dont want to sign any contract. The only thing that can prove i was staying there is a deposit receipt.

recently, the girl's mother wants to visit Singapore. The girl does not want her mother know that she is staying with that boy(sleep on the same bed). Then, she comes to me and ask me move out before her mother's arriving. I was so mad about this and dont want to stay any further. So i moved out in 2 days. After that, i ask them to refund my deposit. But they said i didnot give one month notice so that the deposit will not return to me.

Since we have no contract, i dont think the one month notice rule exits. Is there anyway i can legally get my deposit back?

BTW, the whole unit is rent by the girl, while the deposit receipt is signed by the boy.

Thank you very much for your help