I want to cancel the app I just installed to stop spam calls I do NOT want to pay charges

Cancelling a subscription or deleting an App does not reverse the transaction made.

Unknown Charge?

1. App Purchase
   1. Curious about a Charge? --> If you see an 'itunes.com/bill' or an unfamiliar charge on your statement
   2. If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
2. Subscriptions
   1. You may view a subscription to an app --> See or cancel your subscriptions - Apple Support
   2. You can also request a refund for a recent renewal of an in-app subscription purchase 

Avoid accidental purchases

1. If it is your device then, please --> Use Guided Access with iPhone, iPad, and iPod touch - Apple ... before handing over a device to a child.
2. If it is your child's device then in the future, enable the Ask to Buy feature --> Request and make purchases with Ask to Buy - Apple Support

It could be Phishing

• Beware of --> Phishing & Other Suspicious Emails 
• Know how to --> Identify legitimate emails from the App Store or iTunes Store 
• Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams —> Use these tips to avoid scams and learn what to do if you think your Apple ID has been compromised.

chicken458 Said:

"I want to cancel the app I just installed to stop spam calls I do NOT want to pay charges: I want to cancel app I just loaded to stop spam calls on iPhone"

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Troubleshooting Scam Messages:

Three Thoughts:

A. Use Malwarebytes Mobile Security:

The free version blocks popups. Read the following post to see how to use this software: Blocked numbers - Apple Community

B. Modify your Credentials:

If you suspect activity issues, and interacted with it an any form, then modify the you credentials:

• Modify: your login credentials (Using Both a New eMail and a New Password for each and all sites)
• Associate: a different method of payment to your account
• Enable: Two-Factor Authentication for Apple ID and for all other accounts that have such an applicable option

C. Report this to Apple:

Have a Screenshot of this? Forward a screenshot of this as an attachment to Apple using this eMail address: reportphishing@apple.com. In the comments pane, inform Apple of what the attachment is all about: an eMail containing an attachment of a phishing scam. Use my User Tip: Using the Photos App to Report Scams: - User Tips

Delete the app on your iPhone that you do not want. If you are unable to cancel the subscription or in-app purchases, then Please start here 👉 Refunds, Subscriptions & Billing Questions

Axel F.