hi silent tears, listen to what bedobones is saying , it is exactly what i would say too.

you have two choices,
1. carry on as you are and let your abusers win
or
2. find it in yourself to break the cycle, fight for the grades you deserve, and show your abusers that you are different from them, that you can stand on your own two feet and better yourself without their input!

only you can chose which you want, but i suggest you aim for the second choice even if it is the more difficult to achieve because in the long term it will give you the determination you need for life.