TFA: Changing "Send code by" setting from "SMS" to "Voice Call" - ERROR: Number already exist

TFA: Changing "Send code by" setting from "SMS" to "Voice Call" - ERROR: Number already exist

Hi,

I'm trying to change the TFA " Send code by" setting from " SMS Text Message" to " Voice Call".
Problem: each time I get the error message: Number already exist.

Shouldn't we be able to change this default setting?

Thanks in advance for feedback!


We are after all essentially irrational. — Spock