Why is iMessage not working on my iPhone but works on iPad and Apple Watch?

I’ve tried resetting my network, toggling the on off switch for I message. So I’m not receiving any messages from iPhone users on my phone only one my iPad and watch. I’ve chatted with an Apple agent who could not figure it out, they were trying to get me to senior specialist but I haven’t spoke to them yet. Ivecff so poke to my carrier who tried and they told me to speak with Apple. I’m missing so many text and people aren’t getting my text. HELP

[Re-Titled by Moderator]

Original Title: iMessage Not Working