You might have to restore the backup manually. The user.usage file is part of DirectAdmin's data files that are stored in /usr/local/directadmin/data/users/username
Is it corrupt? Can you extract the files and view it?
If you don't want to to it manually, you might be able to use an existing user.usage file from another user as a template, recreate the file and recompress it the backup/ You might be able to get DirectAdmin to restore it automatically then.