I would just be straight with them, no shouting, no tantrums, no name calling or accusations, just simply lay it down straight. "Look, Mum, Dad, this is important, I need to get on with this, I am trying really hard here to study, these exams are important & hard. I need you to back off and leave me alone to get on with this. I will give 1 hour a day to chores or time with you or whatever but the rest of the time you must let me get on with this. If you don't I will have to go stay at a grandparents/aunts/friends house till the exams because I am seriously stressing that I am going to fail if I continue to try to study here & not be allowed to. PLease understand how important this is & please ttry to leave me alone to get on with it, or I will have to stay elsewhere or defy you & go out to find somewhere quiet." and follow it through. You're not a baby, you can go out without their permission, if they don't let you get on with it just walk out, go to the library or someone else's house & that's that. They need to support you or you need to find a way to support yourself.