Volunteering

If a sports organization you belonged to told you, You HAVE to volunteer for every event they host or else they’ll charge you $100..what would you say or do?? I don’t mind volunteering my time, but when it comes down to being questioned on why I wasn’t there the entire time every one else is, and told that my time won’t count it pisses me off. I’m not volunteering to offset my child’s sports fees either, it’s strictly to help with an event. I feel like this place is confused on what the term “volunteer” means.