Minor account debited for personal loan

My daughter's father sends money every month to my mother for child's school fees into the MINORaccount that my mom opened for. Today, two amounts of R722.91 and R361.46 were debited from the account for supposedly a loan that my mom owes from FNB. I do not understand why a loan that she took is taken from a MINOR account from money that is supposed to pay for her school fees. She went to the branch and the consultant was holding on the line with no luck of going through to the relevant department. Its almost exam time, school fees are outstanding and she will not be able to write. How is money paid into a child's account taken for a loan that has absolutely nothing to do with the child. Whether the adult has signing powers on the account gives no right to FNB to debit the account. And on top of that lines are busy to even get through when the consultant tries to assist.