Hacker buys subscription with his own money on my account, and I recover account

So tthree days ago I received an email that my long forgotten World of Warcraft account was trying to change the password and email. I went back and forth with the "hacker" who was trying to change passwords and the email, until the email and password recovery/changer was disabled due to too many attempts.

So I called the Blizzard World of Warcraft support line, and I was able to get my account back via security questions. When I logged in, I noticed that today a new subscription for $15 monthly was activated, and it was a Visa, which no one in my family uses, therefore couldn't be ours. So I deduced it must be the hacker's.

My question is, would it be illegal to not unsubscribe from the billing?

(Also, as a side-note, the support person said the person who tried to hack into my account was unsuccessful, which brings up the question, how did he do it?)