I bought a new iPhone 5s a couple of weeks ago, and it refuses to connect to 4g. I live within the regular LTE network according to Verizon's coverage map (zip code 13209). I've tried disabling and re-enabling LTE, switching airplane mode on and off, restarting the phone...nothing seems to help. It stays stuck in 3g when I'm not using WiFi. What could be done to fix this?