Refuse to replace Samsung

I upgraded my contract in April 2015 and got a Samsung s6 edge, after 2 weeks I went back to shop confirming it takes 40min to charge then lasts only about 4 hours, gets very hot, when someone phones me the call just gets cut off after while and when I phone someone they can't hear me. They changed a setting and said I must give it some time, after that the phone has already been sent in to repair centre twice without any joy, the phone still has the same problems. When I took it then in today they just refused to replace it and said I must sent it in again and proceed sending it in until it is fixed, every time I must borrow another phone because they also confirmed they can only give me phone that can do phone calls, I am a business women that depends on my phone. They were rude had no sympathy and don't understand that since I upgraded in April I was using a friends phone more than my own but still keep on paying my contract.