Issue with smoking at the rental

Hi, we are renting out a room in 3 room hdb for 5-6months. Landlords brother also lives in the house in one of the rooms and he smokes a lot. When we first moved in we were not told about the smoking situation. In the lease there is a clause that smoking is prohibited. One day my husband saw him smoking in the living room. He told him that I am not okay with smoking. He tried smoking out the window and because of his job he was mostly out. So it went on for few months and then yesterday he was smoking inside the house. So my husband asked the landlord if we can leave in January second week and he said that we have to pay for January and he will not give our security money back. So we agreed to move out in December. Is there any way we can get our security money back?