Finally today I went to his shop and as you know he make all sort of story the technician....bla..bla.  I talk politely saying if he's in my position what will he do.  I also mention to take this case to tribunal user at Shah Alam.  Then only he took a new set and hand over.  I said if the set faulty again, I will ask for my money back.  With his masam muka he agreed.