Because of the way Apple’s subscriptions work, you must stop the auto-renewal with them and request a refund. To cancel your auto-renewal, visit the following link from your iPhone or iPad. And then proceed to stop the auto-renewal. Following this, reach out to Apple and request a refund of the last payment:
Step 1: Locate the invoice receipt email for your iTunes Store purchase and click the “Report Problem” link next to the name of 8fit. Alternatively, if you do not have iTunes on your computer, go to reportaproblem.apple.com to submit a refund request to Apple from your web browser.
Step 2: Sign-in with your Apple ID and then choose an option from the drop-down menu that best describes your problem. You can expect a response from Apple in the next 24-48 hours.
I wish this was easier, but it’s the only option we have on iOS.