Searched the internet and I found some evidence that I may be able to do it through the Box iPhone app. The Box iPhone app referred me to cancel the subscription through the Apple iTunes/App Store. However, there are two problems with this:
The instructions are out of date and do not match the current UI for the App Store/Subscriptions/Apple ID/etc.
My Box subscription is billed directly to my credit card, not through App Store subscription
Just for kicks, I tried everything I could think of to find the App Store subscriptions settings and found no trace of a Box subscription anywhere.
I'm about to file a ticket or email support, but thought I would post here as well. Anybody else having problems with this?
We'll look to clarify this in our articles, but also work on creating clearer instructions for Personal Pro accounts like yours. For now please follow @katrinaa's instruction or if you already submitted a case, our billing team will work with you on getting this set up.