If an invoice was automatically sent on one of your orders, then you have Automatic Shipping Policies set in place. Check your Shipping Settings to confirm!
You have Automatic Shipping Policies in place for one of two reasons: Either you manually added them from your Shipping Settings, or you once clicked this checkbox on an order page:
Clicking that box will create a shipping policy based on the media format and buyer’s country. Using the example from this image above, if the checkbox was clicked, moving forward, any time a UK buyer purchased a Vinyl (Large), an invoice with €10 shipping costs would automatically be issued.
If you do not wish to have this shipping policy in place, simply delete it from your Shipping Settings.