My phone won't receive texts?

I just got an android phone (LG Apex) with US Cellular. But the problem is with some people, I can text just fine, send and receive texts. But some people I will text and never get a reply. And when I talk to them they say they replied but I never did. So I don't understand whats going on? It's really annoying me because it leads both me and the person I was trying to text that we are ignoring each other.