Not happy at all

I have had a problem with my phone ever since I bought it,it switches off by it self ,has short battery life and over heats . I have taken it to Samsung for repairs more tha 3 times and when it comes it does the same thing,,,, we recently I took it there again I think it was the 2nd week of January they have not contacted me to tell me what is the problem ,when I'll be getting my phone . No one is saying anything . Please advise on what I need to do coz I have been waiting for them contact me,they have my email address and alternative contact number.NOT HAPPY AT ALL