Poor service

Last month I took my Samsung S4 into the Gateway Samsung branch as my phone was not staying on. They guy tried something and it didn't come on at all after that. He told me that I need to take the device to the Samsung repair centre in Nandi drive, so I did. A tech from there calls me later in the week to tell me that the board is damaged on the phone and they need the proof of purchase to repair it. I DO NOT HAVE THE PROOF OF PURCHASE as the phone was a gift. I took my phone for repairs earlier this year and I told the agents that I didn't have proof of purchase, they made me fill out a form confirming tthis and proceeded to repair the phone. if I couldn't produce the proof of purchase then, how am I going to get it now.<br> Cant they use the same documentation to repair the phone????