Rein here from Shopify. I appreciate you bringing this up.
It's great to hear you have signed up for the Annual Billing, it is then unlikely to be any subscription charges are to be the root of this charge in this case. We can look at either your Credit Card fees or your Shipping Label purchases for this charge as the amount is not too dissimilar from any other charges you would encounter.
First let's check the billing section of your admin. Down the bottom left of your admin click Settings. From there you can click Billing.
Once here, you will see the billing amount in question mentioned that you have paid. It will highlight if it is fees for Credit Cards or Labels for Shipping and you can view more information by clicking into the charge itself.
For future reference and more information on everything regarding charges within Shopify, you can refer to this article here on the topic.