Refund from an app

So I recently downloaded a app on my phone and I was charged $21 for something I was unaware of, and I didn’t agree to any purchases or subscriptions, but it still charge me for a subscription on the app! I emailed the people on the app and they told me that they refund policy is connected with Apple and that I would have to contact y’all to be able to get my refund back , please get back with me as soon as possible. Thank you.