I'm just really annoyed about this service center,...

I'm just really annoyed about this service center, they don't even know whats the issue of my device. So They have replaced my device, after i get the replaced device and when i used it for less than 30min i used to see the same issue i was facing at my original device. So they keep it for 2days and after that they told me that it was an IOS issue and we didn't found any problem. And when i contacted to the service center they told me that it is a hardware issue and they given false information. After all this i have raised a complaint and i submitted the device to them and now they have replaced the device again. So tomorrow is the day i need to take the device & gonna update very soon....!
Issue: Getting multi-screen with random colors whenever i restart the device .