If you subscribed to ChatGPT through the Apple App Store, your subscription is managed by Apple and will need to be canceled through the subscription plan on your iOS device.
If you wish to cancel your subscription, please follow these steps:
Go to “Settings” on your iPhone
Tap your name
You will be presented with your active subscriptions. Tap on “ChatGPT”
Tap “Cancel Subscription”
Confirm your cancellation on the pop-up window
Deleting your ChatGPT account on the web interface will not cancel your ChatGPT Plus Subscription
Your Apple App Store account will be charged 24 hours prior to the end of the current subscription period
Subscription features will remain in your account until the end of the current paid period after canceling
For detailed instructions on how to cancel an iOS subscription, check out Apple's tutorial here
Please follow this Apple knowledge base article if you would like to request a refund from Apple (in the case that you subscribed to ChatGPT from your iPhone app as opposed to the web interface).