Engine Knocking Noise problems of the 2003 Chevrolet Avalanche

First of all my vehicle is a 2003 chevy. Avalanche, well maintained and only has 62,000 miles. To get started, I was driving down the street when I heard this banging noise, so I pulled into the nearest GMC dealership. They checked the engine out and found out there was absolutely no fluid going into the engine. We were told we needed a new engine so I authorized them to put a new one in. The service manager and a couple of tech's looked at the engine and agreed it was a defect. I contacted GMC immediately because the dealership told me they have a goodwill policy and they felt they should pay something towards the engine. Customer service insisted that I put the engine put back in and have it owed to a chevy dealer. I asked them what the difference was between GMC and a chevy dealer and they could not respond to me. I did not have the vehicle removed because of the cost all I was asking was for them to have a rep. Go to the dealership and look at the engine but they said no. By this time I was very frustrated and angry. I called GMC executive office and spoke to another girl and she assured me she would help me. Well low and behold she said "I didn't bring my vehicle to a chevy dealer therefore they will not help me out financially. . All I want is some financial help from GMC as $6,000. 00 is alot of money and I am on a fixed income, ss only. I had to pay the bill of $6,000 plus $125. 00 for a rental on various charges because I didn't have the cash. It would be greatly appreciated if you could advise me on how to proceed. I sent a certified letter to the president of GMC and he won't even pick up the letter from the post office. I wrote a letter to the detroit press and have heard nothing also. The dealership that repaired my truck also covers the warranties and repairs chevorlet vehicle. So why should I have to tow my vehicle out of there?.