Charged for app that I unsubscribed to

Hi, I downloaded an app a couple of months ago, and because it wasn't helpful, I unsubscribed. Under my subscriptions on my Apple ID this app doesn't even show up. When I log in to check my subscriptions and payment history, the app doesn't show that it charged me. But still, I have been charged, twice, for this app that I have unsubscribed to and doesn't even show under my subscriptions under my Apple ID. When I tried to dispute the transaction with my bank they needed the exact date I unsubscribed, but unfortunately, I don't recall and it doesn't show under my account. I tried calling the company, and they aren't getting back to me. How can I go about getting my money back?