Issues with accessing an account

I am trying to add an old account to my phone, but the account uses two factor authentication which, for as long as I can remember, I have had the same phone number that I've always used for my accounts and don't think I've ever used a different one, yet for some reason the phone number that's linked to this account is NOT my phone number. So when I enter in the account and password correctly it says, "we've sent a code to (***)***-**44" and my phone number should say "(***)***-**42", but when I choose the option "I no longer have access to this phone number" it still requires me to KNOW the phone number before I can change the trusted device. Now at first I assumed that it was just the last 2 digits that got mixed up and tried entering in my phone number just like normal except having "44" instead of "42" but that didn't work, I don't know anyone who's phone number ends in "44", have tried all the numbers that I could think of that are close to that, but nothing works! I cant seem to find any other way to access my account either, no option to answer security questions instead(I'm sure I used security questions for this account too...) no option to use a linked email, nothing. the only option for me to access this account is to KNOW this stupid phone number that I never linked to this account and since I don't know it I cant seem to access my account? can anyone help me out here?