I'm so sorry. That sounds horrible. Is your dad open to any sort of feedback? Maybe something from another source that he might be more open to listening to? As a speech therapist and fellow person who stutters, I've found these videos helpful when I've sent them to parents: [https://www.youtube.com/playlist?list=PL4ohn8hCulK5xHZ76ApiLP7H9WA8yCG6s](https://www.youtube.com/playlist?list=PL4ohn8hCulK5xHZ76ApiLP7H9WA8yCG6s)