Yahoo mail has a MAJOR security flaw

A while ago I bought a new phone number. I went on Yahoo! mail and typed in the phone number in the login. It asked me if I wanted to receive an SMS to gain access. I said yes, and it sent me a verification key or access code via SMS. I typed the code I received. I was surprised that I didn't access my own email, but the email I accessed was actually the email of the previous owner of my new number.

Yahoo! didn't even ask me to type the email address, or the first and last name. It simply sent me the SMS, I typed the code I received, and without asking me to type an email or first and last name, it gave me access to the email of my number's PREVIOUS OWNER. Didn't ask for credentials or email address. This seriously needs to be revised. At minimum Yahoo! should ask me to type the email address or the first and last name before sending me an SMS which contains an access code. This would mean that new owners of a number could gain access to the email of that number's previous owner without being asked any type of security question, or to even type the email address or at minimum to type the first and last name correctly. Please revise this, Yahoo! I am a concerned Yahoo! user, and no I did not look into the email, I logged out. This has happened before to people's Yahoo! accounts. How can we ask Yahoo! to change this?

Simply requiring users to type the email address/credentials before receiving the SMS would solve the problem.

I have contacted support and though Yahoo! said their engineers have been informed they haven't fixed this so far. How should we get them to fix this? Petitions?