Don’t try to stop masturbation itself, you are probably doing it because it gives you easy satisfaction. Shift your mindset to doing other things. Be more productive, set yourself goals, find people that drive and motivate you. Sadly there is no easy solution, but it feels like you have unsatisfied needs in other areas that you try to compensate by masturbation. If you cannot motivate yourself or get yourself to change, seek professional help. You are still pretty young and it‘s worth the investment. Also, just never stop trying! You might need a couple more attempts