Self harm

I don't understand what I am doing wrong. I have cut and burned myself since I was 12, and I'm 17 now. And I can't just seem to stop. And before I was 12, I used to scratch, pinch, and sometimes hit myself with hard things. I want to die more than I know I should. 
I have told my mom about how I feel many times before, and she says that I am just seeking attention, and she will ground me. And I know I need help, but there is no way for me to get it without her knowing. I just don't know what to do, and I know if I don't get help soon, I really will not be able to handle this anymore, and I might do something bad. I just need advice, please. Anyone.