check your purchase history to see what you’ve been billed for.
“If you don’t recognize the amount on your statement, multiple purchases might be grouped into a single transaction. You might not receive a separate email receipt for each purchase. Sometimes the charges appear on your statement a few days after the purchases were made.
In addition to music, movies, TV shows, stickers, and apps purchases (from the iTunes Store and App Store) that are billed at the time of purchase, your statement might also include in-app purchases, pre-ordered music or movies, and automatically renewing subscriptions.”
If you see 'itunes.com/bill' or an unfamiliar charge on your statement
https://support.apple.com/en-us/HT201382
Is it possible you have some apps that were set up to automatic renewals when the free trial ended? Or you failed to cancel a subscription?
To manage subscriptions and turn off Automatic Renewal, follow the instructions here:
View, change, or cancel your subscriptions - Apple Support