S4 can't get fixed or repaired

i have a problem with my samsung s4, that i won in a competition. when i charge it, tells me that i have 100% and as soon as i unplug it shows 83% as well as get hot while i use it. i did visit the repair center in vereeniging, the lady was rude and didn't want to hear what i had to say in the end i just left them. i then drove home and decided to call the samsung call center and explained that i won the phone and don't have any proof of payment or any other proof, they advised me to call the vereeniging center and explain to them, i did that and again they told me that they could not take the phone, so i called the center again to find out what i must do now and then was told that if i don't have any papers then i can't get the phone fixed. then what the heck must i do to get it fixed.