My ex canceled a trip that was paid for on my girlfriend's credit card. When we arrived at the train station to obtain our tickets we were told the tickets were canceled and had to pay even more money to purchase new tickets. Is this legal?

Was he also on that same credit card?

No, He thought I had purchased the tickets on my credit card. He had no idea that it was hers

How did your ex know the credit card number? If the credit card number, the confirmation number, or the transaction number was not given, you need to go after the vendor. By your account, anyone could do this to anyone else. There has to be more to it than that. What's the deal?

How did he cancel the tickets? Was there a ticket for him? Did he cancel through through the train operator or did he cancel the charge?

We need more info to determine legality and liability.