Don’t hang up when they ask what they can do better. Don’t stay with them either. Give them an honest, respectful, but blistering critique explaining why you are leaving and why you will never be back. Be polite, which means they have to keep you on the line. Your discreet example won’t make a blind bit of difference. However, all of these calls are recorded and the larger the sample they get, and the more the call centre staff talk about it, the more likely they are to listen to the feedback.
Source: I review this shit and present it to various management teams for a major Australian company
Why not both?