Well done for saying something. I had many teachers laugh at my stutter during school and I was too scared to say something. As an adult, I now know that you can gently let people know that you stutter. Most of the time, people are apologetic and it will make them think twice about doing it again. Hopefully I can stop them from laughing at someone who will be much more upset about it than me. It is disappointing that your Professor didn’t take as much accountability as you would’ve hoped but us humans have a tendency to go on the defense immediately after being called out for our behaviour. Stick with him and see how he behaves. Good luck with your course!