imessage not working

I have recently updated my iPhone 5S to the iOS 8.3 and now my iMessage and Facetime are not working through my Apple ID. It works for my phone number but not Apple ID which frustrates me as I cannot use it on my iPad Air 2. I tried everything from resetting my phone and iPad, checking the settings, turning it on and off, etc. but nothing works. I often receive the message of Error of a network connection or failure of activation....how do I get it to work again?