Like usaka said, and I will expand.
How did they get caught? Well the butler didn't know that Hajin wasnt there because he wanted to be. The butler thought he worked his way again. So to 'GET RID' of having, he drugs him with a heat induced and throws him into MLs room. The next day, the trauma just breaks MC Hajin. ML knows something is off so he looks at CCTV and finds out what butler did, this also leads him to find ought the servants were starving him and stealing his things. Hajin tries to hurt himself and the guilt really begins bc Levi knows it was his actions that caused this.
ML wanted all the employees to be punished. He wants thier cases to be extended to 5 years hajin was abused by them. He limits thier access to good lawyers and other jobs.
In the meantime they bring in new staff, that wear different clothes (due to trauma) make so everyone has to know and not just barge in.
Then uncle comes in and worsens the trauma. So yeah.
Later you find out that ML is one sided minded to MC. And eventually him almost dying allows the ML to slowly recognize that the ML is trying. And has really chamged

Rn I'm staying only for future grovellingヽ(`Д´)ノ