If a client tells me he can't pay the amount in full, I tell them to pay as much as possible. Also, the way the paying parent gets paid may mean that he may need to make two payments to you each month. So, there might be a decent reason why that happened.
But to specifically answer your question, no, a lawyer's directive to a client cannot override a court order. If the lawyer was simply being defiant, you can contact their licensing authority. But, step back and consider why the lawyer may have advised the ex to do this.