Verizon sending threatening emails to pay or it will goto collections but offers no way to pay.

Hello as the title reads I had a verizon account but I switched over to at&t. Now they have been sending me emails from a Do not reply email. I am in rebuilding credit after a bankruptcy so I'm trying to keep this off my credit. But they offer no way for me to pay. I tried online on the website but when I go through the disconnected way and enter the phone number they say they can't find my account. I tried on the phone via their automated system went as far to enter my social and they say they can not find my account. I tried finding an email or to contact a different way but the only way to contact is to have an account and to sign in but when I try you guessed it says the account doesn't exist. So how can they try to put something on my credit but offer no way to pay.