When I recently changed provider, they assigned a new number to me ; but later on my request they applied my old number. But the new number is still in Settings. How to delete it and replace with my old number ?

I recently changed service provider. At the time they allocated a new phone number to me which later was changed with my previous number.

however. I still see the said new number in my phone Settings And said number appears on my friends phone number when I call them .

How can I delete it and replace it with my old number.