If I understand correctly, you do not have any subscriptions, but you were billed for something. This can happen if you are the organizer of a family sharing group and a purchase was made by one of those members. You can also check to see what the unfamiliar charge was from. I would recommend you read these articles and use them to help troubleshoot the issue.
About Family Sharing purchases
If you're a member of Family Sharing, anything you buy bills directly to the family organizer's account, unless you have gift or store credit. In that case, your store credit is used to pay as much of the bill as possible. If there's a remainder, it bills to the family organizer's payment method.
iTunes Store credit isn't shared with other family members. If the family organizer has a credit on their account and another family member buys something, the cost of that item doesn't deduct from the organizer's iTunes Store credit, but bills the payment method that the organizer has on file.
The family organizer gets the receipts for any of their family member's purchases.
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