Hatchback/liftgate problems of the 2007 Chevrolet Suburban

My 5 year old son was hit on the top of his head with our automatic closing cargo door on our 2007 Chevrolet Suburban when the resistance mechanism failed. Instead of going back up after meeting some resistance the cargo door continued to close on his head resulting in a gash to the top of his head which resulted in 3 staples to the top of his head. I immediately notified gm and it has taken this long to get some assistance. They offered to pay his medical expenses, which were already covered with our military insurance, and 300 for his pain and suffering. We declined the 300 because gm would not take responsibility even going as afar as to say that I may have caused the damage by pulling him out from under the door. When I asked the claims lady if I should have then allowed the cargo door to keep closing on my son's head she said I don't know I wasn't there. I want to warn other parents because accidents happen and the cargo door should not require that much pressure before the resistance mechanism works---my son should not have had to require 3 staples to the top of his head!.