My mom is a pathological liar and I need to tell my stepdad she's been lying to both of us about eachother.

It's a very urgent matter that I let him know what she's up to but I'm not sure how to go about it. It's a lot to tell him over the phone but showing up at the door is a bold move because of a restraining order against me. Also, I'm not sure what is going to happen after I blow the whistle on my mother. She's gonna be in big trouble. Should I just write him a letter? He doesn't have e mail damnit to hell. Help!