Various iPhone6 texting issues

Hello!

I am having three issues with text messaging. I have an iPhone 6 with AT&T as the carrier. I'm hoping someone can help me. I've researched and have not been able to find solutions to my specific problems. Below are the separate issues I'm having. I sincerely appreciate any help you can provide me.

Issue 1:

I receive some, not all, of my iMessages on my iPad but not my iPhone. The thing I find most peculiar about it is that every time it has happened, the person I have received the iPad message from has previously been able to message me on my iPhone, sometimes even that same day. Even after a hard reset, the missing message never appears on my iPhone.

Issue 2:

My cousins and I have an ongoing group message. Of the 4 of us, 2 have iPhones and the other 2 are Galaxy. Very often - nearly everyday - I will receive a message from one of them that is clearly in response to a previous message I never received. If I turn the phone off, then back on, I will get all the messages. If I forget to do that for a day or two, I will literally receive 8 - 10 messages from various people that I never received.

Issue 3:

I have been receiving a message that comes from "unknown" and says "Message not found." I have probably gotten about 15 of these messages over the course of a few months. They do not seem to coincide with the missing texts mentioned above.

So, there it is....my issues. I have tried to find solutions and have not been able to pinpoint my exact problems. I'm not even sure if the issue is with the phone or the carrier. Thank you in advance for any help! I really do appreciate it.

Elle.