Cognizant — offer letter got but date of joining details

Address: 2/118, SIRUVANI MAIN ROAD, Coimbatore, Tamil Nadu, 641010

Hi my neme is vinothini i got a offer letter for juniore tester at april 7th in coimbatore chil sez it park and joining date april 15thbut 2days before i received the mail of joining date extension but i don't received new date of joining mail please send the joining date i called the hr but no reply so please accpet my request and send the joining date