I purchased an App accidentally. How do I stop paying for it!? And it is an automatic renewal which I obviously do not want.

If the App had a price to download, then its a one time purchase and will not charge you again, and there's nothing you need to do unless you want a refund.

Log in to https://reportaproblem.apple.com and raise an issue with the App. There's a refund option there.

If the App was free to download, but had in App purchases / renewable subscriptions, then you need to manually cancel it so it does not renew and charge you. Follow the steps here: View, change, or cancel your subscriptions - Apple Support

Then contact iTunes Billing for a refund: iTunes Store - Contact Us - Apple Support

Click here, follow the instructions, and use this form to ask for a refund.

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