I would suggest that you reach child abuse help lines. They will be able to provide you with useful advice.

Your mother is clearly being abusive, and probably the best way to adress this is to use a neutral intermediate. I think a professional psychotherapist would help, as it would remove her from the dominating position (older, legal tutor, etc).

Also, don't rush to marriage just to escape your mother. That would be a very serious mistake. Take your time to really earn your autonomy, don't use costly shortcuts.

If you still can't get this solved, continue posting here, I think there are plenty of solutions available to you.