Cancel subscription billed by iTunes

[iMore Question]

I recently purchased an HBO Go subscription through iTunes. It is a reoccurring charge on my Amex every month. I now want to cancel it. Amex tells me that if they block the charge from my credit card I will no longer be able to purchase anything from iTunes on this card in the future.
The charge occurs the 4th of every month. It is a pending charge right now for 3/4. I want to cancel the subscription now. How can this be done?

 

[anon(9602380)]

Welcome to iMore. Here is a link to HBO Go on how to cancel your subscription.