To cancel your Peacock TV subscription, call 1-888-653-7618 Peacock TV support go to Plans & Payments, click Cancel Plan, and then check in at peacocktv.com. You must use the settings on the platform, not the Peacock website, to terminate your membership if you signed up through a third party, such as Apple or Google Play.
If you signed up straight from the Peacock website:

If you signed up via a third-party service (like Apple, Google Play, or Roku), you have to cancel via that particular platform. How to Cancel Peacock TV Subscription
Regarding Apple (iPad/iPhone): To locate and terminate Peacock, launch the Settings app, choose Subscriptions, and then press your name or Apple ID.