My iMessage is not activating on my number. I have updated my phone as well

First, check to know whether you have an SMS plan enabled at least for One SMS with your carrier. Contact your Carrier (Cellular Service Provider) the agency who issued the SIM to you

If your iPhone is used with a carrier not found in the wireless carrier articles, make sure you can send and receive international SMS. (One SMS Only)

See the pic below

4 Step Process --> Turn off and restart iMessage and FaceTime (The order/sequence is very important)

1. Go to Settings > Messages and turn off iMessage.
2. Go to Settings > FaceTime and turn off FaceTime.
3. Restart your device.
4. Turn iMessage and FaceTime back on (Watch the GIF hereunder)

Hi, there are a few things to check and try. Check that you are connected to the internet, either wifi or cellular. Also try toggling the iMessage switch to off (Settings>Messages>iMessage ), restart your iPhone then switch iMessage back on. Another to try is go to (Settings>Messages>Send And Receive) Here you will find a list of numbers and email addresses that can send and receive iMessages on your device, look for 'Start New Conversation From' if there isn’t a checkmark next to your phone number, tap on your phone number to activate iMessage for your number. You could also try resetting your network settings, (Settings>General>Reset>Reset Network Settings), please note this last step will erase your wifi passwords. VPN's and bluetooth will be reset to factory default.