iMessage activation problem

I have an iPhone 4s with iOS 9.3 installed on the Vodafone UK network. Last week I noticed iMessages were not sending from my phone number but still from my email address. So I go settings- messages- send & receive, there is no phone number just my email address, I have tried re activating iMessages but no joy. My date & time zones are correct, FaceTime is turned off & I have done reset all settings. My sms is working ok & vodafone are happy everything there end is working ok. Please could someone give me some guidance on what I should do next!