Deleting an app

How do I ensure that an accidentally purchased app is deleted? It’s icon has been deleted from the app screen of my iPad mini but it still appears in subscriptions. I had purchased this free app but it charges after 7 days’ free trial. I checked it out and it’s not an app that I will use as it is too advanced for me. So I want to ensure that it is considered deleted before I am charged a subscription for it. Thank-you.