If you wish to get a refund on the pre-purchase that should be very simple. Here is the direct link with the support menu options chosen for you. Blizzard Support - Contact Support
I am sorry but no, the pack can not be separated. They also don’t issue refunds if content has been used/played to an extent. So if you were playing D3 enough to level some they will categorize it as being functional on your system and “used”.