They're not going to tell you why, and an alleged customer service number will never be authentic. All of this is because this is a company with just over 25,000 employees servicing a user base with over 1.8 billion (that's no typo) users per month. It's impossible to do that, so the vast majority of actions are via algorithm. They won't provide personal service unless you're super-famous and have a ton of followers, like Lady Gaga.
So consider what could be the issue. I suspect it's name-related, as FB is cracking down on odd names. They are also cracking down on multiple accounts as you saw personally.
Try several means of getting in, e. g. laptop, desktop, phone, etc. Provide the requested documents. If you can, get friends to upload recent pictures of you and tag you in them, as FB might ask you to find yourself in pictures.