GM Unwilling to Fix Mistake

We recently bought a 2008 GMC Acadia off a dealership in NY (Albion of NY). The car was advertised to have DVD entertainment and navigation. While the car has both, we soon realized after we drove off the lot, that the radio is broke. It will only play CDs not DVDs and CDs. After much aggrevation we found out that it is the wrong radio all together, and possibly may have been built with the wrong radio at the factory. GM said their warranty only covers replacing the current radio in the car, which of coruse is the wrong one. We have dealt with this for five months and both GM and the dealership refuse to pay for the correct $1600 radio. I have been a loyal GM customer for 12 years, since I was first able to drive at 16. I will never again buy GM, nor will I buy from this dealership. I would hope that with their business in such constraints, they would try to keep all customers, especially loyal ones, happy. Apparently they can't afford a $1600 radio that is rightfully ours. I hope you all consider buying from Ford or a foreign manufacturer before you look at GM.