Feeling suicidal and no one cares?

I'm fifteen and I'm feeling very suicidal. I'm in therapy and my parents know that I'm suicidal but they think its "normal" to feel this way and that I'm "manipulating" them to get attention. I feel like no one cares and everyones given up on me. I honestly don't know what to do anymore. I've talked to my therapist and my parents and they both seem to push away the problem. I think my only way of help to show that i'm serious is to "attempt" suicide. How could I do this?