phone heating up-Blackberry 9320

I purchased my blackberry 9320 6 months ago. It was sent in for repairs 2 months ago reason being the screen had lines and was just going blank! So I sent it in after that. They repaired my phone and gave it back to me. Now I have noticed that the phone heats up within 7 minutes. I am so disappointed because I purchased a blackberry 9320 from game 3 times and returned it due to the same reason. I thought purchasing it from markhams Will be better but its doing the same thing. For my phone to be just 6 months old and having so many problems.I am working and I need to have my phone with me all the time. Price of the phone was R1700.Really unhappy customer and absolutely dissapointed with markhams and vodacom