I recovered some money from the site. I made a mistake somewhere on the form and that led to an email which I believe contained a phone number I used to get clarification about what they were questioning. So, I would suggest submitting the form with any information you can and then hope for a response from them which may provide you a way to contact a human. It is a slow process, good luck.

This sounds like someone is scamming you.

It's a HUGE hassle for anything complex like that. I gave up trying to recover my deceased grandfather's account because they wouldn't accept the estate paperwork.

Does he have a tax ID? Use that. If I recall correctly it's less used for identification and more for tax purposes if taxes are owed so they can issue a 1099. I deal with it fairly frequently for estates and such and if there are years of interest or dividends accrued you can owe taxes on those amounts.

call them. they are very helpful and helped me recover funds from a deceased relative