How to remove old phone number and add new one in iMessage?

[itsMohsinK]

I have changed my phone number and its hell removing the old number from my iMessage I have done everything like switching off iMessage on old number then resetting network settings changing apple id password and its still showing my old number greyed and not showing my new number at all!

 

[qbnkelt]

I have changed my phone number and its hell removing the old number from my iMessage I have done everything like switching off iMessage on old number then resetting network settings changing apple id password and its still showing my old number greyed and not showing my new number at all!

I would try this sequence.

Insert the new sim with the new phone number.
Settings > Messages>Turn off iMessage.
General > Reset > Reset Network Settings.
Turn iPhone back on
Go to Settings > Messages>Turn ON iMessage to have your phone recognised and the SIM verified.

If this sequence doesn't help I would consider backing up your data and wipe your device and then do a restore from back up.