mobile

Hey guys, I bought a second hand AT&T Moto X 2014 off ebay about a week ago with a clean IMEI. I unlocked the phone by buying a code online, but since then have not been able to get a stable signal. I purchased a new TMobile nano card, and had it activated. I'll get cell service for about 3 minutes, and can make calls, send a text... then the phone will get no service whatsoever for the rest of the day. I'll get surprise pockets of service for several minutes once or twice a day.
I spent some time with the TMobile technicians, who have registered the IMEI, have done a master restore (not sure what that meant) sent several signal downloads to the sim, and ultimately said the issue is with the phone. I also tried my wifes ATT sim card and rebooted, still resulting in no service on ATT either. The Moto X is running 5.02. I've tried messing with the APN settings in various formats that I've seen online. My new sim works with my Nexus 5 perfectly.
I contacted the ebay seller, who is willing to refund 50% of the purchase due to unlocking the phone online. Do I pretty much have a bricked phone? I can't seem to find a solution and have gone back to using my nexus 5 with a shattered screen.
Thanks for the help.