Unable to repair phone

I upgraded my contract end of January 2016 to Samsung Galaxy Core, not even a month later the phoned malfunctioned. I handed it in for repairs, two weeks later I got the phone back and it was STILL broken. I handed it back the next day and the last communication I had regarding the repair was 10/3/2016......I went to the branch two times when they said the phone will be repaired and it wasn't.!!!!!! I want a NEW phone!!! If they can't repair the phone in more than a month what are the chances I will be battling for the rest of my two year contract. This is not acceptable!!