Sony Ericsson Mobile — valid purchase, but declined by company

sir,
i purchased a sony eriricson mobile from one of the dealers in alwarthirunagar, chennai, bearing the name of asian network. after three months my cell phone got repaired, and i approached the same person for the warranty claim. only after this i came to know that the sony erricson declined my handset claiming that it was not manufactured by their company and that i am not eliglible for any warranty claims. then again i approached the person from where i purchased the mobile. but till date he has shown deaf ears to my complaints. in this regard i would like to know how am i suppose to proceed to seek justice.
thanking you,
with regards,
venky