You are very welcome.
Do not give up with GM, make sure you have opened a claim, and get the number, you will need it.
Really stress the point that you purchased an after market warranty from a GM dealership, and they are denying this too. Let them know you are upset, and want this to be taken care of, see how that goes.
If you start to lose traction, on this approach, start down the road of them helping you with the cost, this is when you will need help from the dealerships service manager, hope you have a good relationship with the dealer. They can do a lot more in helping you that they will let on.