If your syllabus is complete, you've done your previous year questions and mock tests, you could try taking a week long break. Stay away from social media, don't watch Netflix or anime. Read story books and talk to friends and relatives. Go for long walks at a park or even better near a lake. Get as much sunlight as you can.
You've been at it for a long enough time to feel really frustrated. Your deprovement is an evidence of that. Remember every exam is independent of the other. Forgive yourself for failing at a previous attempt.
Also try to cut off bad habbits slowly.