I need my money back

Not sure what you mean by "from this one app". How does it have it? Do you mean you wish a refund for an app you bought? Or do you mean there's a subscription?

Request a refund for an App Store or iTunes Store purchase - https://support.apple.com/HT204084

Report a Problem to request a refund - https://reportaproblem.apple.com/?s=6

If a reporting a problem request is unsuccessful you can also try:

Other ways to contact iTunes Support:

https://www.apple.com/emea/support/itunes/contact.html

or

https://support.apple.com/country-selector/itunes

Apple's terms of purchase for most countries are effectively, "All Transactions are final" (check terms at: http://www.apple.com/legal/internet-services/itunes/ ). Apple may refund on a case by case basis, but realize they can also say no.

For a subscription:

You must first cancel any subscription automatic renewal (if you simply delete an app this does not cancel subscriptions):

See or cancel your subscriptions [subscription automatic renewal] - "If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends." At this stage the renewal is considered a purchase. Canceling a subscription does not automatically start a refund since the existing subscription will normally continue until the end of its term and then just not renew. - https://support.apple.com/HT202039

Now review:

Report A Problem to ask for a refund. Click on this link --> https://reportaproblem.apple.com/?s=6

If Report A Problem does not work for a subscription refund you may have to make a special request using one of the contact links provided earlier.