I’m guessing you probably won’t win a chargeback unless you can show that you sent them a letter telling them to cancel (and because of this, they actually will cancel if you send them a letter).

I think another aspect of this problem is that credit cards don’t just let you mark a transaction as “don’t allow any more of these.” Of course that probably wouldn’t solve the problem. The gyms would probably just continue charging you and eventually send you to debt collection.