I just got an iPhone 5 yesterday and I can't get an internet connection on it at all. It shows an E where it would normally show the 4G. Actually, sometimes it does say "4G" and I still am unable to connect to the internet. The only time it works is when I'm connected to wifi. I already went to the T-Mobile store and the person updated the carrier which should've fixed it, but obviously did not. What can I do to fix this?