Why can't I receive a picture message?

Okay so I have iPhone 5 on AT&T and my friend who I think is on Verizon (not sure) tryed to send me a message and I never received it? I don't know why I mean I can get them from other people but never him… He tryed multiple times and I still never got it… Does anyone know how to fix this I need help… Please and thank you so much.

On setting
go on messages
turn imessage on

  • Why won't my iPhone 3G send this picture message? My iPhone's sent pictures before, but it's not sending this one. It's not even failing, it's just been 'sending' for, i don't know, fifteen hours. I just tried to send another one to my friend's iPod, but it's doing the same thing. What the *** is up? It's really pissing me off because now I can't send any messages to this person because these are still freaking 'sending'.
  • Why is my iPhone not notifying me as soon as I receive a message? I'm not good at explaining but what I mean is like sometimes I get a text and it says it's been received like 35 minutes ago but it's only just come through on my phone… Anyone know why or what I can do to stop it? It doesn't happen all the time but it's been happening quite a bit the past few days and I'm not sure why but it's annoying because people think I'm ignoring them or they worry!
  • Why is my iphone making the message tone but no message? My iphone, for the first ever time made the message tone and I have no message? There's no app on my phone that makes the same sound either I have checked, apart from tweet on settings, but I don't even have twitter… I received a message 20 Minuits before this happened but I read it and replied… I have a lot of storage on my phone so it can't be that either… So what is it?
  • Why don't I receive alerts or a notification when I receive a text and I already checked my settings? I adjusted my setting and even put the ringer and notifications on and put the volume and ringer on and I receive no alert, no pop up, alert or notification when someone texts me. Why? This is the iPhone X! I went to the cell phone/ carrier store and they didn't help me. They said to go to the apple store or check the settings. I already adjusted the settings. So what do I do now?