Are you sure you bought it through the App Store? Typically a subscription not appearing there means you bought it directly from Microsoft and you need to follow their procedure for canceling the service.
This support article explains how to cancel a subscription from Apple on an Apple mobile device, Mac, PC, and online (see the Android section) ➔ If you want to cancel a subscription from Apple - Apple Support
Notes:
• You might need to scroll down to find the Cancel Subscription button.
• If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew. An "Expires" date (instead of "Renews") means the current subscription has been canceled but will work until the expiration date. "Resubscribe" (or Renew) is just in case you change your mind about having it end.
• Deleting an app does not cancel a subscription.
• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.
• Free trials will usually automatically turn into paid subscriptions unless you cancel in time.
• If you don't have an Apple device, see the options near the bottom of the support document.
• Many subscriptions are set to renew automatically until you intentionally cancel them.
If you can’t find the subscription that you want to cancel, use this shortcut to jump to the section about what to do. --> If you want to cancel a subscription from Apple - Apple Support If this is a subscription not made through Apple, “you might have bought the subscription from another company. To find out which company bills you, check your bank or credit card statement. To cancel the subscription, you must contact the company that bills you for the subscription.” About purchases not billed through the App Store or the App Store’s In-App Purchase system - Apple Support
If you still can't find a subscription or still have problems, contact Apple Support using this issue-specific link at the end of the section. --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63006&category_id=SC0060&symptom_id=23208
Scroll down to where you can request a chat session or a phone call.
As for deleting the app(s), you do not say what hardware you are using.
Refer to this support article to learn how to delete apps on your iPhone, iPad, and iPod touch. --> Delete apps on your iPhone or iPad - Apple Support
Delete or uninstall apps on Mac - Apple Support