bad after sale service

I opened an 24 month contract with a S7 edge Samsung cell phone in January 2017. After 2 months the battery of the phone got so hot that it cracked my screen. They fixed it but after another 2 months the back of my cellphone got burnt black by the hot battery, This went on with another cracked screen and problems every 2 to 3 months. In January 2018 my phone went in for the 5th time. This time I got notified that it would cost me R9218.94. I tried to reason with them that the phone was giving problems from the start and they admitted that it was a factory fault but they still want me to pay. Now I have a phone I cannot use but still have to pay for the rest of this year. I had to take out another contract at Cell C so I can have a phone.