My ext hard drive is full, but I can not see files created with deleted Norton 360 Backup Set Names

I'm new at this, so I hope I'm doing it correctly.  My ext hard drive is full of backups that I have created over time using Norton 360.  I need to delete some backups. I called Norton and they walked me through Norton Backup Drive and I thought I was on my way.  But that only shows the two Backup Sets that I currently have.  I had created and deleted Backup Set Names over the years.   How do I see the back files on my ext hard drive that were created with Backup Set Names that I have deleted? 

 

What do I do now?