cant replace my tab from last 5 months

Location/place: Sahibabad, Ghaziabad

Name of company/service: Pentaltech Pvt. Ltd

I Purchased BSNL Penta ws802c 2g on date 28.12.2012 from Madan Mobile lajpat nagar sahibabad, invoice no. 1547, but its functions are failed. then i summited it to service center National Watch & Communication 85,86,jassi building,railway road, bazaria ghaziabad 201001 U.P on date 22/2/2013 after 15 days they get back to me my tab but the problem still not solved. then again i submitted it to the same service center 20/3/2013, but on 13/07/2013 it cant get it. I also send complaint through email to Mr. Divakar Mishra and [email protected] but i can’t get satisfying answer from these two.
So I request you please submit my complaint and take nessary action against my complaint. this is my humble request to you.