How can you get your child off of a step parent's health insurance?

My child is on his step-mother's health insurance. She won't give me an insurance card so I have to pay for his RX and pay when I take him to the doctor. I want to get him off her insurance so I can get insurance on him myself. I have NO idea how she got his social security number because his dad doesn't know it. How can I have him dropped from her coverage so I can get my own on him?|||I don't know why you would have to drop him from her insurance. It seems that if he was sick or hurt you would take him to the dr. and have the insurance to cover it, the step mother wouldn't even have to know he was sick or hurt or went to the dr. I just don't see how him being on her insurance helps her, she has to pay for him to be on the insurance. Of course if he is visiting his father and something happens to him than the insurance she has on him would be helpful. You could also find out if having 2 insurances would pay for everything like he gets sick and the dr. visit is $100, your copay is $50 would her insurance pay the other $50 and vice versa if he was at her house?