Why have I been charged 4 times this month?

You do not say where you see this purchase. If you see it in an email or a message, and if you can not see it using the methods discussed in the link(s) below, there is the possibility you are being scammed. Click on this link to read how to "Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams" --> https://support.apple.com/HT204759

Click on this link to read what to do "If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement" --> https://support.apple.com/HT201382 Note, if you are a Family Sharing organizer, purchases or subscriptions made by another family member may be charged to your card but will not appear under your purchase history or subscriptions. Ask family members about those or check your receipts.

If you need more help:

iTunes [Store] Support - Use this form for assistance with account and billing, code redemption, or purchase questions --> https://support.apple.com/en-euro/itunes-contact

or

Worldwide iTunes support --> https://support.apple.com/country-selector/itunes

iTunes Store - Contact Us - Official Apple Support

This is a user-to-user technical support site operated by Apple, no on here has any information regarding your account or how to contact you. Click on the link I provided above.