Need to change phone number on iphone 15

And where are you seeing this erroneous number exactly?

The eSim is the one that determines the phone number. If its wrong, only your service provider can fix that.

Does your eSim reflect the correct number in Settings ➜ Phone ➜ My Number?

Registered where exactly?

Normally, the phone number comes from your sim card. Contact your service provider if the sim card needs to be updated.

Contact your cellular carrier.