Bad service at makro vanderbilpark

Hello i just recently bought a 65 inch samsung flat screen on black friday last year using my makro credit card , i later returned the screen in January because it was too big for my living area , so i returned the tv sealed and they gave me a 55 inch tv screen which obviously costs less than the 65inch , I've been making my monthly payments but it seems as if the price im still paying for is for the 65inch tv makro has refused to help me with my problem with them coz it seems to me im paying the price for the 65 inch tv and not the one im currently using . So i would like to know what should I do to get help regarding my problem