ANSWER:

It is their mistake for allowing him to be disrespectful and still provide him with food and service. Your mother shouldn’t clean or cook for him until he behaves and act like a grownup man. They should cut the internet access on him and not pay his mobile phone till he mans up.

https://islamqa.info/en/answers/210875/how-should-the-family-deal-with-a-disobedient-son

QUESTION: My brother is 19years old. He dont talk with his parents. If they want to talk, he abuse them. My mother sends food to his room. He is alwz in his room locked. He dont go to masjid. Alwz in his room playing in laptop. My mother cries for him. Makes dua. Sometimes he abuse mother without any reason. His anger is always on high. Is there any solutn to this in a islamic way. Becz we wont go to shirk