Shocking Repairs to Phone

I took in my Samsung Galaxy S4 to be repaired for a cracked screen on Sun 15/03/2015 at Rosebank Mall. The phone which is under warranty had experienced no issues before the cracked screen . I handed in my phone and spent 30minutes waiting for it to be repaired. Once I received the phone back, I noticed that it was getting extremely hot while I walked around the mall, which never happened before this screen replacement. I went back to the store after about 15mins to alert the technician to this fact, he told me that he was now off-duty and I must bring it in the next day. I live and work in Pretoria and only brought it to Rosebank that day since they had the particular screen in stock. Since I had a meeting in Jhb city the next day, I said I would stop by on my way back. The phone got so hot I was forced to switch it off a number of times to cool it down. The next day I brought it in and the technician said the operating system needed updating. This didn't solve the heating problem at all, in fact it caused a new problem where my phone has no signal for extended periods, making me miss calls and msgs. I am very disappointed in Samsung and demand that the phone be repaired.