Cellular Data says searching.

My cellular data on my iPhone 6 has said "searching" for two days now. I use AT&T and no one else on my family's plan is having this issue. Their cellular data, calls, texts, etc. are working just fine. I finally backed up my iPhone to my computer, returned it to factory settings, and now it is not connecting to to the server, therefore, I cannot even activate my phone. I have been to AT&T already and they have done everything they can do in order to try to reset the settings. it must be an issue with the phone. I need my phone ASAP for work. I don't know what else to do. The closest Apple store is an hour away!