How do I cancel an app auto-renewal on my iPhone 6?

I

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how do i cancel an app auto-renewal on iphone 6

How do i cancel auto renewal if in the app store and in itunes store there is no option for "manage subscriptions" it says manage itunes newsletters and special offers but no subscriptions. there is also no subscriptions tab on my Macbook itunes store and the app continues to charge me money every 10 days ??
please help