money back from sony ericsson

Location/place: ahmedabad

Name of company/service: sony ericsson w8 e16i phone

i buy sony ericsson w8 e16i mobile from venus electronic on 11feb 2012.
from 3rd month of purchasing my mobile has screen blinking problem,restart problem and screen active for long time. (mother board problem) i send my phone to sony service center at mobile care swastik char rasta,opp choice restarent, navrangpura, ahmedabad.they change motherboard and give back my mobile.after 25 days same problem continue. now i want replacement but sony ericsson company says no to replacement even i have 6 month warranty for my w8 e16i mobile.now i want to take legal action against company and i want my money back.my trust on sony ericsson is 100% gone.