Your child may have subscribed to it in which case under Family Sharing payment structure you may have to pay for it but the child has the subscription under their account and has to cancel it.
Use this link to read about how to learn "How to cancel a subscription from Apple." - Cancel a subscription from Apple - Apple Support - "If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends."
For unfamiliar charges work your way through the steps in this link If you see 'apple.com/bill' on your billing statement - Apple Support
Prime suspects for unusual charges are subscriptions and purchases made by family members under Family Sharing (if applicable). These will not show in your purchase history but may appear on your payment card. Your email receipt will show the purchaser's Apple ID but details will have to be viewed from the purchaser's account.
"If the subscription that you want to cancel is not listed", click here --> Cancel a subscription from Apple - Apple Support
If you still can't find a subscription, contact Apple Support using the link at the end of the support article.
If you do recognize it and have canceled the subscription and wish a refund: Apple's terms of purchase in the USA are, "All Transactions are final" (Legal - Apple Media Services - Apple ), but some countries have different laws so check terms for your country at: Legal - Apple Media Services - Apple If sales are final then it is Apple's decision if they want to grant a refund. You can always ask, and people do get refunds on a case by case basis, but Apple can also say no.
Click on this link to read about how to "Request a refund for apps or content that you bought from Apple" --> Request a refund for apps or content that you bought from Apple - Apple Support
If you still have problems, click here --> Choose your country or region - Official Apple Support Select your country, then a product.