Bad experiences with the Samsung s8 and customer service

Hi, I have a Samsung Galaxy S8 of which I'm having a very bad experience with. The phone heated up and thereafter produced 2 gold spots on the screen, I was skeptical about the usage if it might explode so I then proceeded to go to the Samsung repair centre in riverhorse place, Durban. They have replaced me with a new unit and now I am getting sticky touch and the phone heats up badly. It is terribly slow and I am uncomfortable with its behavior when I need to use it urgently. I am disappointed by the fact that I have to go to Samsung for the phone to be checked up and then they will tell me what's next. This is time consuming and a inconvenience to me. I need help to sort this issue out or have a courier service come to my house by Samsung to sort this issue. Thank you.