[Resolved]  Nokia 2505 CDMA — not working

dear sir,
i bought nokia 2505 cdma phone on 24 april 2009 from cell world shop klk state hyderabad.within one two days problem is began.the problem is that while we using mobile it automitically switchoff.in one hours 3 to 4 times switchoff.after 3 days i reqeuset replace the handset to above said shop where i purchase it.but they refused to replace and advice me repair it at nokia care centre.
then i approch nokia care center on 29april 2009.they take my hand set and after 15 working days they return hand set.and told me that your mobile is repaired all problems gone. but problem is continue.3 month later second time i approch nokia care center .this time also they 15 working days for repairing .but the problem is not solve now.what i have to do pls suggest me