I have this problem with paypal:
Made an account about 10 years ago with email address x, mobile telephone number y, bank debit card z with some security questions thrown in.
I cannot remember my password from 10 years ago so I need to reset it.
If I try to reset it, they want to send me an sms otp to the mobile number from 10 years ago which I no longer have. Obviously I cannot update the mobile number if I cannot log in.
Another option they give me is to enter some portion of the debit card number that was linked to the account. I no longer have that account from that specific bank, nor have the old cards laying around.
Another thing they offered was for me to fill out the answers to the security questions, but I absolutely hate these and always fill in random characters by mashing my keyboard, so no go here.
In their help guide they say you can contact support if you cannot log in at all, but you have to log a support ticket.... which requires me to log in. Last time I gave up after 30 minutes of poking around their site to try and find a way to speak/email a human that can help me get back into the account, since almost every path leads back to the login screen which wants my debit card number from 10 years ago.
So I've started ignoring paypal now. All their emails that I still get goes in the trash and I will never use them again. Keep in mind this was a business account linked to a business bank debit card (it was the only way back then to link to an account in my country, and only one bank offered the integration, since then things have become much more reasonable (cheaper business credit cards = international ease)).
I'm fully willing (well not anymore) to send them a copy of my national id card to unlock my account while we speak on the phone, but they seem to have no path to support their clients unless logged in. Maybe its been fixed by now but I no longer care about it enough. If you build systems with an auth mechanism, please cater to all the unhappy paths your clients might fall into. I'm not one of those people who will go scream on twitter to get help, I just silently walk away and you lose a client. It's that simple. I'm not expecting them to treat me like a king, I just wanted to log into their site, that's all.