Short answer
The most common reason is that auto-renew was still turned on when the next billing date arrived.
When you first launch the app, activating a subscription is required to install the eSIM. If it is not canceled, it renews automatically.
To stop future renewals
Open the app → Settings → Manage Subscription → Сancel the subscription.
If you want a charge reviewed
Contact support with:
receipt/invoice number or screenshot;
charge date and amount;
email used in the app.
Important
Turning off auto-renew does not automatically refund a past charge. Support will review the request.