Why won't LTE work on my iPhone 5s?

Just got the iPhone 5s for US Cellular. Data usage is part of my plan. However, when I'm not connected to Wi-Fi, the internet does not work. It says I'm connected to LTE, and I have 4-5 bars of service, yet, it does not work. Any advice or answers as to what is going on and how I can fix it?

What did us cellular tell you?