Phone number already exists

Phone number already exists

I just set up my Zoho account this morning. When I tried to login this afternoon, I was told my password was incorrect. I reset it. The very next screen prompted me to " Add Mobile Number" for my email address and phone number. I'd already added a number this morning for two-factor authentication. Nevertheless, I entered the requested information, and clicked "Send Code" and got the message that "This phone number already exists". 

How do I go forward from here?