Phone number

[Tandod]

I moved to sky mobile when I got a new phone keeping my old number. This phone seems to have 2 registered number my old number (which I kept) and a new number. My friends were having to text me off the new number as when they texted my old number it did not work but they had to call me off my old number. Now it seems someone else is registered to the new number that is registered to my phone as when my friends go to text me someone else reply's. Now if I text my friends it comes up with no number and my email address. But people can call me on my old number. In settings the new number is on there and it does not let me change it. How do I fix this. 

[twilight+princess]

When changing the number I would add +44 then the number omitting the 0 at the beginning. This worked for me on iPhone 14 Pro Max after swapping from iPhone X.