The original number is embedded onto the sim card, you can either request another sim card and it will be embedded with your old number you transfered.
I've not done this but apparently you can put your sim card into an iPhone and its capable of changing the embedded number on the sim card (google will tell you how to do this) obviously you'd need access to an iPhone.
It has only become a problem when I tried to add my bank card to my Google Wallet. My bank say the number asking for authorisation is the number in my settings, which is not the number my bank recognises as my own number. I will speak to my bank again to see what can be done. Alternatively, I will speak to Vodafone. Thanks for the advice, have a fantastic weekend 😀