They are wrong. If you subscribe to HBO, you get HBO HD as part of the HBO subscription; same for Showtime. The HD Package is not required.
Just ignore what they say; the computer handles it; they don't. Cancel the HD Package, and you'll still have HBO HD and/or Showtime HD if you subscribe to HBO and/or Showtime, respectively.
Just ignore what they say; the computer handles it; they don't. Cancel the HD Package, and you'll still have HBO HD and/or Showtime HD if you subscribe to HBO and/or Showtime, respectively.