"You disgust me."
Apart from your mother is very mean and she obviously has no clue what you are going through and it took a lot of guts for you to talk to her about it. You have more courage than I ever would! X
Try talking to a friend, a school counsellor, or a nurse at school. Explain your problem and say that you're seeking help, but don't know where to get it. Add that your mother isn't being very cooperative, you don't need to get into details, no one needs to know about your relationship with your mother.
I was never bulimic myself, but I know quite a few people who were/are, and I have seen how destructive it can be, both to your both and your mind. The fact that you're looking for help is very positive already, and I honestly hope you get the help you need and deserve. If you ever need someone to just listen, PM me.
edit: some parents are so convinced that their child is perfect, healthy, happy and has everything they could possibly need that they refuse to see that something's wrong. That might be the case, too. To a parent, recognising those problems is like publicly admitting they failed as a mother/father.
Edit: I'm also sorry to see that I am the only one who gave a helpful and supportive response.
Owned.
Your mom's a bitch.
Honestly, You should get help from other people. Try friends, or your school counselor.