How do I scream for help?

I feel my depression getting worse.
I know I need help.
I just don't know how to tell my mom and dad.
If I tell my mom,she'll just laugh at me and say,"You're not depressed!"
I can't blame her for thinking that.I've been hiding my depression for 2 years with a smile.
I don't know how to tell her.
I've seriously been thinking about suicide.How am I going to kill myself?
We get free therapy with our insurance plan,but the first step I need to take is telling my family.
I just don't know how to do it.
A black hole is sucking my soul in,and I don't know how I'm going to get it out.
Before it's too late.