Is charging a gift card without money illegal?

Recently, I got Facebook credits to advertise my business. To get the credits I had to register my credit card. Obviously, I knew what they were trying to do (Charge my card with however much if I forget to cancel it) So I registered an old gift card with no money left on it and it worked. The problem is, is it illegal that they charged like $3 to a card that had $0 available? the charges went through successfully.