We need to know why your parents wanted this school. Cost? Prestige? Location?
We need to know why you hate it so much.
Finally you need to meet with someone to assess clinical depression and how much of a role that may be playing here. Medication may enable you to stay.
Since your parents are paying, you can remain under their control and stay, you can call their bluff and leave with risk of no support. or you can leave and support yourself.
I would like to hear that you have accessed help and possibly meds before making this decision.
Withdrawing may give you relief but it will only be momentary. You can escape the school but not the overall situation this way.