Can't log in, unable to resolve

I created a Facebook account back in February for the first time. When I created the account, the phone number I used for authentication purposes was my work-issued cell phone. After retiring on May 31, I was trying to link my Facebook account to a different email address, and I guess this triggered something security related, and the Facebook system asked me to authenticate by providing the code sent to my cell phone. The problem there, as you can see, is that I had returned that phone to my employer when I retired, so I was unable to enter the authentication code. I tried resetting my password, which I was able to do, but the last step of that process is to also enter the authentication code sent to the same phone that I no longer have. So here I am ----- stuck. I have no idea what to do. I was shocked to learn that Facebook apparently has no customer support phone number to call. At least I haven't found one. I read that you can also request your "trusted friends" to help you reset your login, but this was the first I had heard of that. Point being, I have no one designated as a "trusted friend." I have sent two snailmail letters to Facebook using their Menlo Park address that can be found on the Internet, but I have received no response. I can't believe there is no way to resolve this, which is why I'm reaching out to anyone here who might be able to help me. You might be wondering if I've called my old employer to see if I can get access to that old phone? Yes, I've tried that. They said the phone has since been "recycled." I've also tried calling and texting the old number to see if whoever has it now could simply give me the authentication code when it comes in, but the number is no longer working. One of the things I had noticed in the short time I was on Facebook before I hosed myself is that there is the occasional person with more that one account. Someone suggested that I just create a new account with a new email address, but I refuse to do that. I feel like an idiot enough already without announcing to the world that I'm so dumb with this stuff that I locked myself out and had to create a new account.

If anyone knows of a solution or a secret Facebook email address or phone number where I can get help--or maybe there's a Facebook employee who will see this and have mercy on me---whatever help I can get will be greatly appreciated!