As suggested above, GM and the dealer have no obligation to fix this issue.
My limited experience with extended warranties is that they have specific rules and terms outlined in your contract. You should have read and understood these terms before you bought the warranty.
Now, read those rules and terms. They will describe the process for making a claim, how to do so and whats covered. They also indicate your obligations as well.
These firms are merciless. If you don't follow the terms and conditions they will not honour a claim. So, read the rules, find out where your claim has gone bad and correct it.