how to remove a personal account connected to MFA if my iPhone was stolen?

I am trying to login to pay a bill, that I set up 2 step verification (MFA app)

however the original phone that I set it up with was stolen.

every time I try to sign in, it generates a code for me to enter, but it gets sent to my old device

so I don't receive it to my brand new phone via the authenticator app

I even called the business several times and they keep having me reset my password but that is not the problem.

after I enter my password it wants the secondary security code sent to MFA