Why can't I receive texts off non-iPhone users?

I have an iPhone 5s, and it's in perfect condition To start off with, however i can't receive text messages off non-Iphone users?

I've tried every single thing the Internet has to offer!

My iMessage works perfectly fine and I can send and recieve them just others whi don't have an iPhone can't text me back because I dont get them?

This has only been happening since last night and this morning?

Please help!