My Device Is "Searching" for carrier (No Service)

I have an iPhone 6 plus, running on iTunes 9.2.1 (newest update). As of yesterday around 4pm my phone started to search for a network and will not connect. I went to the AT&T store and they put a new sim card in my phone and it still will not work. Can some one please help me?

I have toggled airplane mode, took out sim card and cleaned it, reset network settings and finally I erased all settings and content (after a back up) and restored to factory settings. STILL does not have service.

Any Advice?

Thanks friends.

Travis Fox