How to cancel 10$ for 10 subscriptions of seventeen by accident?

I was signing up to win some free stuff on www.seventeen.com/freebies. A fill out pop up came up that you could block out but i kinda forgot to. After i signed up to win some stuff it was like "We will send your order of 10 subscriptions for $10 and bill you".I was like :O. I tried cancelling but it said this order can't be canceled. I think this is sooo stupid. I dont want 10 magazines. Please help. How do i get out of thisss? How do i cancel it??