Someone Help. Cant send or receive Pictures and i cant send or receive group texts

I have a Nokia Lumia 635. I've called att and Microsoft about my problems and they didn't help me. For some reason I can't send or receive pictures and the same things happens with group texts. I thought it may be because I don't have enough data but when I bought more data I still have the problem. Any time I try to send a picture or a group text it will start to go through then I get a notification saying that it failed. When people to send me pictures or bring me into a group text it will say downloading media content and then it stops. Someone please help me. I dont know how to fix this.