iMessage does not connect

Set up imessage and facetime after change of number.  

Settings, Messages, Turn off iMessage 

Settings, Face Time, Turn off Face Time 

Restart the phone. 

Settings, Messages, Turn on iMessage, SMS, MMS 

Settings, Messages, send & Receive, Start new conversations from,  select your Apple ID which should now be there. 

Settings, Face Time, Turn on Face Time 

If you still can't send or receive messages on your iPhone, iPad, or iPod touch read this: 

If you can't send or receive messages on your iPhone or iPad - Apple Support 

If you have activation problems see here 

See If you can't turn on or sign in to iMessage or FaceTime – Apple Support (UK)