You cannot cancel a purchase. You will have to pay for them. Then you can request a refund.
Here's how to request an app or media refund from Apple (From: Request a refund for apps or content that you bought from Apple - Apple Support - see the article for more detail.)
1. Sign in to https://reportaproblem.apple.com
2. Tap or click "I'd like to," then choose "Request a refund."
3. Choose the reason why you want a refund, then choose Next.
4. Choose the app, subscription, or other item, then choose Submit.
If you were charged for a subscription that you no longer want, you can also cancel the subscription using the directions in this article --> If you want to cancel a subscription from Apple - Apple Support
If you are having problems with unauthorized purchases being made on your device you may wish to always require a password for App Store and iTunes purchases.
Click here ➔ Require a password for App Store and iTunes purchases - Apple Support
Remember that the people responding on the forums do not work for Apple. We are Apple products users like yourself. If you want to talk to Apple about this, refer to this page for Apple Support features ➞ Contact - Official Apple Support
If the presented options do not resolve your issue, keep experimenting with any series of selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
This page has telephone numbers for contacting Apple for support and service ➞ Contact Apple for support and service - Apple Support