general problems of the 1996 Chevrolet Impala

I bought my 1996 Impala ss brand new, and every year since then in the winter time I loose the heat. The dealer, while the car was still under warranty, would flush the heater core and sometimes replace it yearly. The problem still is not fixed, and I have lost the heat in the car again and the dealer will no longer fix the problem because they claim it is out of warranty even though they have all of the service records showing the history of the problem. I think this is totally unfair to the owner, and I have talked to many caprice/impala ss owners of this year who are going through the same problem. Chevy knows of the problem but does nothing to correct it, and now the owners are left with the bill and if you cannot afford to have them fix it you drive in a cold car. If they do not know what is causing this problem, then chevy/dealership should be responsible for flushing or replacing my heater core(whatever is needed to restore the heat) for as long as I own the car. I need some help with this, I am only a small guy fighting a giant. Any assistance you can provide would be greatly appreciated. Thanks kjb. Ts.