Xiaomi India — mi4i mobile mein

The problem is that few days back the screen of my device mi4i broken, so i gave it to the mi exclusive service centre, c-14, first floor, sec-f, aligang, kapoorthala chauraha universal book center, opp-puma store, but they didn't gave me any reference no for service and after checking the phone they said that the phone's motherboard is defective, ie, they have stolen my motherboard and replaced it with a defective motherboard. I have registered my complaint regarding the same in october 2017, but still no response from them, they are frauds.