I think my existence is a waste of money
Is there a reason you believe this?
For my parents, I've cost quite a lot of money.
Your parents are probably proud to invest in you, it's bad to think of your existence as a waste. You should have confidence in yourself and thin highly of yourself.
That's not the case, my parents just don't love me and therefore hate the money they spend on me.
If you feel they really think that way it might be helpful to ask them how they really feel or go to family therapy. If you don't think things will work out it might be good to make a plan for the future and maybe go to school or find a job to support your self.