Cs21a530 Tv Of Samsung — defective tv supplied and replacement not given.

Dear Sir,
I had purchased a Samsung CS21A530 TV in September 2008. From the very begining there were colour patches comming on the screen, which appear when the tv is run for a few hours. The engineer from Samsung had visited and taken the tv back to their works for repairing twice but to no solution. Then vervally they agreed to provide a replacement but till date neithor they have provided the replacement nor they respond to the numerous mails which I have sent to them. I sincerely feel that it is a design defect and hence they are not responding to it.
Need your openion in this matter.