What should i do if i change my phone number

Assuming you have changed (are changing) your phone number, there are many operations you need to do on your iPhone. This one is a check list (perhaps not exhaustive) of things to do:

• Change your number in Settings>Phone>My number...
• Change your number in iMessages & Facetime
• Change your number managing your account and trusted devices (see that particular section) for two factor authentication code:--> Two-factor authentication for Apple ID - Apple Support
• Change your profiles for homebanking app(s) so that they can send you proper codes (do the same for all your signed in application, if needed).
• Send the new number to all (or part of) your contacts.

Regards

Giulio