Ask HN: What to do when Facebook 2FA is hijacked to an unknown WhatsApp account?

It seems weird to post for help here but I don't really know where else to ask.

I received an email from a friend saying they saw a weird comment posted from my Facebook account. My account was protected using 2FA, but somehow was hijacked, and they changed the 2FA to be a WhatsApp account. I don't use WhatsApp, and I don't have any way to turn-off or change my 2FA on my Facebook/Meta account.

I've gone through all the help pages and cannot find any way to contact support to help get this fixed. Any suggestions?