How do I tell my mom im atheist.?

I used to be a goodie goodie christian and then I did some research on christianity. I found alot of interesting facts! I talked to my history teacher and she confirmed them. I never really believed in all that ****! I just did it cuz I was born a Christian and never questioned it until now! Please help me because I already told her but she doesn't seem to take it seriously. She thinks I'm going through a phase. But I strongly belove there is no god. And question to myself why I'm talking to the sky. It all just seems stupid to me(no affiance to y'all who believe in it). Also btw I am aware of the difference between agnostic and atheist.I honestly don't get how people can believe in something that they can't verify!!(no affence!)