I'm not receiving text messages of numbers not saved in my iphone.

For the last two weeks I've been waiting for a text message of a unknown number and I'm not receiving those messages. I had the chance to ask someone (who is not in my contacts) to send me a text message and the message doesn't appear in my cellphone. I even checked and it says delivered.

I'm receiving text messages from people who is in my contacts. And the carrier.

thanks