Hell is Other People(2018)

Jong-U Yun is a young man in his 20s who moves to Seoul and rents a cheap room in a run-down building because he is low on money. The place is dilapidated and the residents are creepy, but Jong-U decides to stay until he has enough money to move elsewhere. However, when mysterious events occur, Jong-U realizes that the residents may be more suspicious than they seemed.

(Sources: WEBTOON, edited)