Phone number activation for iMessage

I recently took my Sim out of my phone, and when I inserted it back, and tried to activate my iMessage with my phone number, I was getting the error activation unsuccessful. I tried everything in the Apple articles and nothing seems to work. iMessage Will only use my Apple ID for iMessage. I tried resetting my phone, restarting, and it’s still not working. Why can’t I no longer use my phone number for iMessage? Please note that my phone number was working before with iMessage. What could possibly cause this?