Never mind, problem fixed. I figured out where I was going wrong.
I believe I was trying to upload the files to the new users directory before all of the changes to the account were going through, or something...
I decided to FTP into the new user's account one more time before I sent off the support request and the files I uploaded perviously weren't there. Just that blank HTML file.
I'm not really sure if I was just being completly daft and uploading to the old user account (and I'm fairly sure I wasn't) or if DH took a little longer than the 2 hours it says to make the changes, but that doesn't matter, it's fixed now.