Locked Out of Email for Months

I have had AT&T U-Verse for probably 15 years. When I first got this service I made an “att.net” email. A couple years ago U-Verse was bought out in my state and replaced with Frontier. Since then I had an issue remembering my password and have been locked out ever since.

I guess I tried my password incorrectly one too many times. And now I am not allowed back in until I change the password. However, when I go the the change password option, the only option is to call a 1-800 number for assistance. I am not very tech savvy and was not asked 15 years ago to provide a phone number backup. It does not even give an option to enter answers to security questions. 

I have called the 1-800 number several times and have been told the landline number linked to my account is incorrect. I have had the same landline number my entire life. I have essentially been told there is nothing that can be done for me. 

I am feeling extremely frustrated. I have my password, and when I enter it the only option given is to reset my password, but it won’t let me. I have all the necessary information to prove I am the account holder. This has been my only email used for well over a decade. I have very important and time sensitive emails on there that I cannot access and I need to be able to as soon as possible. There must be some solution to let me back into my email. I have tried clearing the cache and change different browsers and still nothing. Please someone help me, this is extremely important!