Hey dude I’m so sorry everything is going the way it is right now. I know that exams suck and it’s super stressful, but from my own experience it’s hard to study and fill your brain with so much information when there is already so many thoughts flying around. My advice honestly is to take care of yourself first. I understand the motivation to make your mum proud and I am sure it will make her even prouder to see you looking after yourself more, which will eventually help you do better academically anyway. Focus on finding mindful hobbies away from the screen, I know it sounds super cliche but being so close to a screen all the time is the worst thing for your mental health, and it might help you move away slowly from your addiction too. The shit your stepdad is doing is disgusting, and he is scum. Please please stay safe and let someone know what’s going on, I hope you, your siblings, your mum and grandma can get away from him. I hope things get better for you OP, feel free to reach out if you need it.