Taking money from bank account

Hello, I'm Annaliisa

My cousin Gaira just purchased app called Minecraft from App Store. We put my moms bank account on Purchased Methods, but soon my mom came into our room and showed us, that 15.98€ has been randomly taken from her bank account. While Minecraft is only half of that price. She is only one who has the account on her phone and she didn't buy anything more. Can you please tell me what is going on and if you can't do anything then I would ask refund.

Sincerly, Annaliisa