If it has already renewed it is too late to cancel (for that renewal period) but you should cancel it before it renews again in the future. You can also try to get a refund.
To see what the app is, be aware that this is primarily a user-to-user support forum; other Apple users like you. We don't have access to information about charges to your account. Apple has a support article about charges — see each of the steps in the following instructions. They include information on contacting Apple Support if the other steps don't help. See: If you see 'apple.com/bill' on your billing statement - Apple Support
There is an Apple article with information about requesting refunds. Click on the following link: Request a refund for apps or content that you bought from Apple - Apple Support
To cancel future renewals, see: If you want to cancel a subscription from Apple - Apple Support