Unfortunately, an order is an order-- so unless your order has a cap or a "reasonableness clause", you stuck with the way the order is worded.... for now.  It seems like your ex is racking up the extracurricular activity to bill, which could impact your ability to pay regular child support.  Instead of risking a contempt action, go ahead and file for a modification of your child support orders and ask the court to place some type of limits on the extracurricular activity expenses.