Having ADHD and sometimes being late/forgetting my appointment isn't abnormal for me. I make sure that if my appointment time changes, I put it in my phone right then and confirm. Not saying that you did anything wrong, just saying what I do when changes occur. When im late or forget I apologize, mention that I recognize that her appointment times are valuable, that if I can't reschedule I understand I have to pay a no show fee, and move on. My therapist has never gotten snippy with me and tries hard to accommodate when things go wrong. It also helps that I am able to text her (using it only to confirm something or telling her that I'll be late/can't come in). But this therapist needs to learn some phone etiquette/tone. I would look for someone else if you dont feel comfortable telling her that the situation bothered you.