<human>: Summarize the given text in a few sentences.

I graduated high school in 2012 from a large public school in Texas. The JV coach always had problems with me due to: lack of time spent on his team (I went almost straight to varsity when I started playing), being uninterested in playing on his club team outside of school, and eventually my dad founding his own club team out of frustration from the political nature of both school and club teams - which caused his team to lose valuable players.

Now I live out of state, however this coach was promoted to varsity volleyball coach. He taunts my sister in front of all of her teammates about my performance. His latest comment was that I was only "a semi-effective player in high school". 

These comments have been going strong for close to two years now. My worry is that my sister will drop out of volleyball due to his bullying. I want to contact the athletic director, but I am worried that my complaints will be thrown straight in the waste basket due to my age. What can I do to make this stop?
<bot>: How can I stop my old high school volleyball coach from bullying/ embarrassing my little sister in front of her team due to his resentment for my dad and I?