Thanks for coming back and confirming that for us.
As you've changed the date the direct debit is coming out to a later date, it means your new bill will be generated later than the previous one meaning there would be some pro rata charges on there for the gap. I think the wording 'package change' is a little incorrect however could be the closest code the team had.
If you would like me to check the bill and confirm this in more detail then we'll need to pass data protection with you so I have sent you a private message regarding this and will investigate further once I receive your reply. Just click on the little plum envelope at the top right hand side of the page to access your inbox.