Mobile number not being recognised

Basically, I have started a new contract and had a temporary number for a day but since then my old number has been carried over. However, my number has been removed from being able to use it for iMessage and only the temporary number is showing? Hope someone can advise me in what to do. My phone number is still the correct number but when it comes to texting it is not. My number isn’t even an option on the send and receive within the settings.