how do i cancel my linkedin premium subscription

There are instructions on this page for managing and stopping auto-renewing subscriptions : Manage your auto-renewing subscriptions.

You can try the 'report a problem' page to contact iTunes Support and see if they will cancel it and refund or credit you : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

Mine doesn't show up in my subscriptions, but the free period ends tomorrow. I don't want to be hit with the 50 bucks. It's not value added to me. Is it not an active subscription until I begin to pay it? I want to cancel it. The instructions put me into a data loop. I go to linkedin, click through to apple, log in, and go to settings, and the subscription to linkedin premium doesn't show. (yet)

If it's not showing on your account (you only have the one iTunes account ?) then you could try contacting iTunes Support and see if they can see it on it and if they can stop it starting charging