Testing Auto-Renewing In-App Purchases in a Sandbox Environment

I have an app where content is downloaded on a weekly basis and hence using auto-renewal subscriptions is the best option. Once a user signs up for a weekly subscription, it is charged on a weekly basis until they opt out.

I researched how to unsubscribe and I read that there is no api call or no other way to implement this from within the application. The user must manually disable it from iTunes and App Store. It's true?

Q: I am testing with a sandboxed account, so is there a way to manage subscriptions. Should you stop subscribing to this particular app? I want to turn off the weekly subscription and then try again to turn it on from within the app. I could not disconnect it from the device. Is this because I'm using a sandbox account?

Answer, please! Thanks in advance!