What do I do if I accidentally order a SECOND subscription to Seventeen magazine?

I was signing up for the little sweepstakes things, and they make it so easy for you to order another subscription for ten dollars. I just forgot to click the button that said I already have a subscription. Well, I need to cancel it, because my dad will FLIP, when he sees the bill. I've tried calling customer service, but they never answer the phone. It doesn't even ring. Someone else said that after a couple days, they'll send you an email with the subscription number on it, that way I can enter that on the website and cancel it before my dad gets the bill? Is that true? HELP!