First of all, I want to say that I'm not so attached to my PC, but somehow find it "degrading".
I (m / 14) have recently brought some bad grades home (maths SA 6, chemistry SA 4 etc) but never expected such a grade. Personally, I take that really easy, because my average is so at 2.8. My mother now threatens to take away the PC, or put in the basement that the "controlled" expires.
So. What to do next? I could just watch Netflix and come down. Could. I'm currently looking with my parents "House of Money".
Would you - in this situation - watch the series without the parents, and then maybe look again or say that there's no more interest or what would you do?
You could just invest your time learning and improving your grades. Then you do not have to live with your mother's sanctions anymore.
Take a look at the talk by Prof. Dr. Med. Dr. Spitzer on youtube to:
e.g. The film at 42:50
That should show up at school. So everyone sees how stupid he makes himself, or what he could be and instead do so not to fool so quickly.
You might even consider investing more time learning instead of watching Netflix.