How do I cancel a subscription for an app I purchased from the App Store, but it does not show up in my Subscriptions?

I looked in the app for the cancel option first, but there wasn’t one. Then I looked under My Subscriptions and didn’t find the app there. The only thing I could find it under was in my Purchase History. I also checked in the app for Help/Support, but the info on canceling subscriptions doesn’t work in my case since it doesn’t show up in My Subscriptions. They are trying to charge me for a year subscription that I don’t want. Any other suggestions would be most appreciated.