What did you find from reviewing your purchase history and subscriptions. If you see a subscription there, you need to cancel it on your device.
If you used a free trial and did not cancel at least 24 hours before the trial period ended, then you have agreed to the subscription by double clicking the side button, followed by verification with FaceID/TouchID or Passcode. If someone else has the Passcode to your device, then they are authorized to make purchases.
If you are the Family Organizer using Purchase Sharing, then members of your plan are authorized to use your payment method.
If you do not see the charges on your Apple Account or use Purchase Sharing, then you need to consider that your payment method has been compromised. For a fraudulent charge, those are disputed through the bank that issued the card. The bank is the one that approves any charge made with a card and retailers are required to accept the transaction through the agreement they have with the PNO(Mastercard, VISA, American Express, etc).