Smoking problem

I have this shared house with 6 other roommates. The one next to my room seems to have smoking problem and I have noticed the smell leaking out through the door. Even though I reported it to the landlord in which he addressed right onto the next day, as well as the lease mentioning smoking is prohibited, I caught them smoking almost everyday at night.

What should I do? I don’t want to be a snitcher but at the same time I feel like the problem is not fully addressed and there’s no method to effectively stop them smoking. I’m not eating in the kitchen (1st floor) and I can smell it all the way from here (their room is in the 2nd floor).