We don’t have control over money transactions. Apple does that themselves. They handle it all from purchases, making changes and canceling subscriptions.
Apple has recently improved user's access:
Their instructions are located here:
About Video Storage: Free users have less storage than Pro users. Most folks clean up their "Videos & Pictures" pages before Pro expires.
-Download and save the videos that you want to keep.
-Delete videos to free up space. There is a "Delete all unstarred videos" option in Video Settings.
I'm sorry to hear that you would like to cancel your subscription. We would be very interested to know why. Maybe there is something we can do to make our user experience even better.