That does seem very odd. To figure out what exactly might be going on we'd need to take a deeper look into the order. With that being said, the best next step is to reach out to an advisor on our support team who can do that. We're not able to look into account specifics via the Community for privacy and security reasons.
When you reach out if you could have the rate you think you should be charged, the rate which is actually charged and the example at hand, it would be a huge help to speed up the process.