Im punished at home when im already on lock down at school! wtf?

im in grade 9 in a strict all girls catholic school and ever since i started high school i got loads of detention. like more than 30..for stuff like starting fights, talking during class after being given several warnings, cheating, and cursing. my parents always give me hell every time i come home late cause of a detention. they took away my tv and my computer for a bit. right now im grounded now and for the whole summer!. i dont think they should punish me because im already on lockdown at school. its so unfair! what do you think? the detentions at my school are 2 hours. they can be 2 hours or 1 hour or a half hour depending on the severity of what i do wrong. i got 2 hours for the rest of the year.