Unable to unlock phone

I had my phone with AT&T & my father set up the account. he has passed now, so i don't know my account number or the email he used. I can't submit an unlock request online, and customer service either runs me in circles or straight up hangs up on me. I know my phone number that is no longer in service, and my IMEI number. Is that not enough?! I already have a new SIM with a new carrier, but AT&T will not unlock my phone due to not knowing the account number. Please help.