what exactly do you want to do
( not it isnt legal - certainly in civil law - I doubt you cd do that in criminal law or else every one wd be doing - "rain stops play- keeping the moolah then"
Money back - write a nice letter regretting the cancellations and asking for a refund
Suppose the PTA is run by Miss Taylor who always was odd when you were there and has matured into a mad rabid old bat. And you wish to give her a good kicking to make up for all the times ....
Hmm I will have to think about that one ....