iMessage activation failed with my phone number on iPhone 13 Pro Max

I have been using iMessage with my phone number (NTC) for a while, however, my iMessage is not working anymore. When I try to activate it using my mobile number, it says activation failed. Further, I used to get my normal text message in my Mac however, I am not able to get the regular message in my Mac, is it due to the issue in the iMessage???

[Re-Titled by Moderator]