General Motors — certified pre-owned 2016 canyon rear sliding window latch

On 10/21/17 I purchased a certified pre-owned 2016 GMC Canyon. It had 6025 miles. It is still under the bumper-to-bumper warranty. The vehicle was purchased at Motor City GMC, in Bakersfield, CA. This dealership is nearly 75 miles from my home. On November 11, I noticed the rear sliding window latch was missing. This creates a situation in which I cannot secure my vehicle. I first went to AV Chevy in Lancaster CA, they indicated I had to take it to the dealership where I purchased the vehicle, because it's a warranty item. I called my sales person, he said to send him photos of the rear window, in which I did. The afternoon of 13 Nov, I received a call from who I believe was the service manager Tim Miller, who said I had waited too long. How can that be if the vehicle is still under it's warranty? I would like the latch replaced or the window replaced.