Nokia
Phone not working properly

I have purchased nokia3110c on 01/09

and right after two days of purchasing it start poor function. It restarts if any content taken from bluetooth or from computer.when the music library updated it restart 3 to 4 times. I have also submitted my mobile for 1 month to higher technitions who repaired the phone but again after 1 week it start giving problem. Kindly solve it.