Lumia 710
Cant operate 3g and in some calls cant end them and i have to restart the phone

I have tried my best and can't get 3g working on this phone.i called my service provider several times but they say the problem lies with the phone.

Secondly during some calls i can't end them and the phone hangs Then I have to restart the phone. I bought this phone on 13th Feb and from the very day this phone has put me to great agony.

Please solve my problem at the earliest.