Unable to Log Into Email...AT ALL

I have had my AT&T email account for around 15 years now, and I've had issues with it from the beginning.  For starters, my email will work fine for months or years, and then all of a sudden, none of my email clients (PC app, mobile phone, etc.) can access it, and it tells me I need to update my password.  Put in the same password I've been using, and it rejects it.  So, I have to log into the AT&T website and change my password, in which I can then start using it again.

A few days ago, my email suddenly stopped working again on all devices, so I assumed it was the same old thing.  I went to log into my email through the Yahoo login page, but this time, I'm never asked for my password.  Once I enter my email address, it then brings me to a captcha.  Once I complete the captcha, I'm taken to a page that tells me I need to enter a code that was emailed to the email address I'm trying to log into.  Well...if I could get into that email account, I wouldn't be where I'm at...so, I click on the option to "Try another way."  Upon clicking that, I'm immediately taken to a page that says I've entered the verification code wrong too many times, and to try again tomorrow.  What?!  I never even entered it once, let alone too many times!  I tried logging in via Firefox, both regular and incognito mode, Chrome, both regular and private, and Edge, both regular and private.  I've tried clearing browser cache on all browsers, restarting my PC, and nothing.  I even tried logging in through my phone, both on and off of WiFi, and it's same exact thing.

So, I go to log into my AT&T account to change the password there, but most of the time I'm taken to a login page that shows my email address, but also shows it as "Signed in," so I click it, where it will either taken me a page that says "Logout successful," or it takes me to a page that asks me to update my profile info, with the only missing info being my phone number.  The problem with this is that I haven't had AT&T wireless phone service in a year, and you cannot add a non-AT&T wireless number to your account.  When I try to add my phone number here, it sends me a verification code just fine, but the moment I enter it, it state that I cannot add a non-AT&T number to my account, and completely stops.  Go through the process again, and instead of entering the code it sends me, I click on "Take me to my account," where it will either actually take me to my account, or will just repeat the same crappy process over and over, repeatedly.  Once in my account, I can change my security questions, password, etc., but they still don't work to get into my email.

Now, I use Thunderbird to access my AT&T email on my PC, and I have to use a secure email key for this, which I'm quite familiar with doing.  I can go into my account and see the active key, delete the key, and assign a new key, as I've had to do numerous time before over the years, but the new key doesn't work.

I even called AT&T Support today, waited for an hour for a callback, sat on the phone with this person for an hour, having me try different things, and still not working.  He then suggested I go to www.att.net/myemailinfo and try resetting my password there, which I did and did not work, as well as submitting a web ticket through that, which I've done, and now waiting for someone to get back to me.  Throughout this call, the guy stated that he can see my account, that it's not locked, but that even had was having some weird behavior out of it while accessing my account.  Before hanging up, the guy even told me he recommends creating a new email account and changing all of my accounts over to use that new email.

At this point, I don't know what to do, because this is my primary email that I use my billing accounts and such, but I'll be danged if I will create another AT&T email account; never again!  I'm just worried that the moment I go into my accounts to change my email address to a new one, I'm going to start getting them wanting to send me a verification link to my AT&T email, which I can't access, and I'll be stuck trying to figure out how to fix those accounts as well.

Why is email so difficult for AT&T to actually get a handle on?  Especially because I have another Yahoo email account that I've had MUCH longer than my AT&T one (since Yahoo mail came out in 1997), and I have literally never once had an issue with accessing it.

Anyone else having this issue, or know of a solution?  I'm at my wits end here, and once I get this figured out (if ever), I will move everything away from this email account and never look back, but I'm stuck with the issue of having to figure this out before I can move away.