Why extra charge is taken on every time app purchase?

If you mean something costs more than the displayed price, in the USA taxes are added on to displayed prices at the time of payment.

If it is a separate charge you do not recognize, the support article "If you see 'apple.com/bill' on your billing statement" explains how you can check your iTunes and App Stores purchase history, cancel subscriptions, and track possible sources of unrecognized Apple charges you may see on a bill. These may be purchases by family members if you are an organizer of a Family Sharing group, or possibly a second Apple ID you use. The article also provides a specific link for contacting Apple if you cannot trace the source of charges. Click on this link to read this article ➞ https://support.apple.com/HT201382 If you use Apple Card you may find this document helpful too: 'If you see an Apple Services charge you don't recognize on your Apple Card' ➞ https://support.apple.com/HT210618

Other possibilities to consider (not all may apply in your situation):

- Unanticipated amounts may be grouped charges ( https://support.apple.com/HT201359 ).

- Purchases can be made with your ID if your Apple ID is compromised (what to do ➞ https://support.apple.com/HT204145 ) or somebody else has access to your device (require purchase password ➞ https://support.apple.com/HT204030 ).

- If you only see a charge in emails or texts that are not official Apple receipts, it is likely phishing attempts ( https://support.apple.com/HT204759 ).

- If you are absolutely certain neither you, nor Apple, nor a Family Sharing member can account for a charge and it ONLY appears on a bill for a charge card you alone control, you may have been the victim of card fraud. Contact your financial institution.

- Small amounts of ~$1 may be an authorization hold that will be refunded (pending charge ➞ https://support.apple.com/HT201292 ).

If a purchase is listed in your purchase history and you want to ask for a refund, click on this link to "Request a refund for apps or content that you bought from Apple" --> https://support.apple.com/HT204084

If a reporting a problem request is unsuccessful or you have another issue you can also try clicking here ➞ https://support.apple.com/choose-country-region/media-services Select your country, then a product.

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world."

Click here --> https://support.apple.com/HT201232

This link to 'Subscriptions and Billing' has a different layout of some (but NOT all) of the information provided above --> https://support.apple.com/billing