Happy to hear that this has been resolved since originally posting, thanks for keeping us updated. I’ll mark your answer as the accepted solution for others who may discover this topic!
In the future, you can always view a detailed breakdown of your bill under Settings > Billing in your Shopify admin. Simply select a recent bill and click Download to view a detailed PDF breakdown of the bill. This will explain where any unknown charges may be coming from; it will state the details and charges for your subscription, apps, shipping labels, and transaction fees.