The basic issue is you are making purchases you can't pay for. Stop shopping. ;-) I'm not surprised about your friends having the same problem. Many people have this problem and just need to learn to not buy things they cannot afford.
Apple is charging you because you have things you haven't paid for yet. If you add a payment method they take the opportunity to charge you for amounts you owe. There isn't anything unusual about this; Apple is following normal business practices. If you don't know what these purchases are, have a look at your purchase history. You may have subscriptions running that you didn't know were running. cancel those if you don't want them.
Once you have paid off what you owe, Apple will stop charging you until you buy something more.
Read this support article for directions about how to see your purchase history in the App Store or iTunes Store [mobile device, computer, or web] --> View your purchase history for the App Store and other Apple media services - Apple Support
This support article explains how to cancel a subscription from Apple on an Apple mobile device, Mac, PC, and online ➔ If you want to cancel a subscription from Apple - Apple Support
Notes:
• You might need to scroll down to find the Cancel Subscription button.
• If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew. An "Expires" date (instead of "Renews") means the current subscription has been canceled but will work until the expiration date. "Resubscribe" (or Renew) is just in case you change your mind about having it end.
• Deleting an app does not cancel a subscription.
• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.
• If you don't have an Apple device, see the options near the bottom of the support document.
• Many subscriptions are set to renew automatically until you intentionally cancel them.
If you can’t find the subscription that you want to cancel, use this shortcut to jump to the section about what to do. --> If you want to cancel a subscription from Apple - Apple Support
If this is a subscription not made through Apple, read—> If you want to cancel a subscription from Apple - Apple Support
If you still can't find a subscription or still have problems, contact Apple Support using this issue-specific link at the end of the section. --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63006&category_id=SC0060&symptom_id=23208
Scroll down to where you can request a chat session or a phone call.
Alternatively, see a list of Apple phone numbers around the world ➔ Contact Apple for support and service - Apple Support