The great thing about e-books is you can download them anywhere.  The frustrating thing can be that sometimes "anywhere" doesn't have a very good internet connection.  Something that can really help you is a download manager.  FireFox has one built-in that can resume your download if it is interrupted.  You can also download a manager program like DAP or FDM.  There are a number of these tools out there.

Try installing one, then log into your account again and allow the download manager to try capture the file.  This usually happens automatically after a manager is installed.  Then if your internet connection is disconnected, your new manager can re-try again once you are connected again without having to start everything from the beginning.