Used "hide email", but can't sign in to company; Apple won't forward password reset email!

I read both articles, but they do not address this problem, which I will attempt to restate.

1. To use the device I purchased, I set it up with an app. The app asked me to set up an account, which I did via "Sign in with Apple". That allowed me to use my Apple ID and my Apple ID password. But I also selected "Hide My Email."
2. Some things I wanted to do were not allowed by the app itself, but instead had to be done on the company's website -- after signing in to my account.
3. At the company's website, I could not sign in with my Apple ID -- that email was not recognized. Instead, I had to use my randomized unique email address. "Fine," said the website. "We recognize that email. What's your password?" But my Apple ID password was not recognized.
4. Therefore, I clicked "Forgot my password", and the company (says they) sent me a Password Reset email -- which should have gone to the randomized unique email address (at Apple) and been forwarded to me.
5. Even after trying steps 3 & 4 multiple times, I have never received the Password Reset email.

So I appear to be stuck. I cannot access my account on the company's website without setting up a password that goes with the randomized unique password, and the Password Reset email does not make it to me.

Neither of the articles above addresses this problem. They both assume you're always signing in at the same place you originally did, using the "Sign in with Apple" process. In this case, "Sign in with Apple" is not offered on the company's website, only on the app -- and that appears to be the main problem with the process.

OK, thanks. I tried contacting their support staff via the App Store on my phone; result was "they'll get back to me within 48 hours." We'll see, and I'll update this thread with whatever happens. Thanks for the suggestion.

Incidentally, my EDIT failed in my last entry, so entering it here. In the penultimate paragraph:

Change from

" ... without setting up a password that goes with the randomized unique password,"

Change to

" ... without setting up a password that goes with the randomized unique email address,"