New iphone not receiving certain people's imessages
I recently bought a new iphone 8 and when I activated the new iphone, my old phone (iphone 6s) was still receiving certain text messages. I then went back and disabled imessage and facetime on the old phone and logged out of my apple id, but instead of certain messages still being sent to the old phone and not the new phone, now I am not receiving text messages from certain people at all. My new iphone has both send and receive messages enabled to my apple id and phone number so I do not understand why I am still having an issue.
What makes this a problem is, I don't know who may be trying to text me and not realize I am not receiving their messages. Not everyone understand that your can send an imessage as a text message, which does then go through. If I text someone whose texts aren't being sent to me, it seems to override and fix whatever the problem is, but I cannot go through all of my contacts and send a text just to fix an issue that may or may not be occurring since the issue seems to be completely random... I have even restored the old phone to factory settings.
Any help on this issue would be greatly appreciated!
iPhone 8, iOS 12.0.1