GM used to have a Customer Relations or Customer Service phone number, maybe they still do. I think it was more for resolving problems with dealers who are providing poor service, rather than problems with GM itself.

I used it once many years ago, when I was trying to get a Cheverolet repaired under warranty and the dealer wouldn't fix it. After several trips to the dealer to fix the same problem, I called the Customer Service number and described the problem. They told me, "We will take care of it". A few hours later I got a call from the dealer, it was all "I'm sorry sir..., We will fix it right it sir..." . And they really did finally fix the problem.

If they are still around, it might be worth a call. I think the number was in the vehicle manual somewhere.