how i cancel a payment that wasn’t purchased from me?

How do you know it was made on your Apple account? If you got an email saying it was that was a scam. See: Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams

A purchase cannot be made on your account by anyone unless they know your Apple ID and password. If you think your Apple ID has been stolen see: If you think your Apple ID has been compromised - Apple Support

You can check to see if the purchase was really made here: Get help with an item purchased from the App Store, iTunes Store, or iBooks Store - Apple Support

If you don't see the purchase when you go here: Get help with an item purchased from the App Store, iTunes Store, or iBooks Store - Apple Support then yes, they are scams. If you have clicked on a link in any of those messages and entered any personal data change your Apple ID password IMMEDIATELY.

Visit If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support