That's the one thing I wouldn't do, if* your idea of not backing down is giving them an attitude right back. You don't know if the person responding to you is having a bad day or what his or her situation is to make him or her act that way. If this one thing would rile you up and the admissions committee remembers that you called and acted this way, what would they think about you as a future physical therapist?
If a future patient you had wasn't agreeable and acted out, would you try to act as professionally as possible or give him or her lip back? That's the question you want to ask yourself when dealing with people that may potentially have a say in your admission.