I sit on the supplier advisory council for GM CCA (Customer Care and Aftersales, used to be called Service Parts Operations) and interface with them on a regular basis at the director and executive director level. I won't release names and email addresses because I won't jeopardize my relationship with these people, but I will forward an email to a couple of individuals who will take it to the top of the ladder. They are very passionate about resolving issues like this.
Send an email to me at email@example.com
describing your experience and issues in detail. Include pictures and a link to your Facebook page, but stick to the facts. Leave out the emotional criticisms of GM and the people you have been dealing with. Include your contact information.
I will forward your email to the appropriate people.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)