Underage SSI

Im only 15 but I get a check and I have since like5th grade, I never got anything from it. Now my dads the holder because.my mom has somw federal punishment I dont really know. But my dad gives me the money every month because my mom never uses it.on m only for herselfe. we all live.in my grandparents household so my mom doesnt have any bills to pay. When I have the money I pay for clothes shoes and.other personal items, when she has it shr buys all kinds.of stuff for herself. Now she is threatening to take it away again and then I wont be able to get anything I need. So is it really illegal for me to hold the money as.she says? Or is she.just lying for money?