I went to Mexico and when I came back to the states, my cell service was not working properly. I could not send or receive texts/calls. I would have to restart my phone or use my airplane mode feature to reset my phone. It would then work for a moment, but then go back to not functioning. I didn't use a different SIM card, I used the hotel WiFi and the roaming services only. Why is this happening and how do I fix my phone?!