You are right, we can see that you did successfully invite 6 people as it is recorded in our system. Your account wasn't automatically upgraded, but it should have been. I have manually upgraded your account to the standard account level and we will look into this bug.
We'll check if this affected anyone else, it may have, and we'll fix that with an update in the next few days.
Thanks for bringing this to our attention. And I believe your situation has been resolved, please check to ensure that.