Who is the page administrator? Next step is to tell them to remove the post.
Have you identified the person making the comments and they page administrator?
The comments are not on a page. They have been made by an individual in a private group.
Since these comments have been made, this person has opened another account (individual profile not page) in a name that clearly isn't a persons name with the sole person of posting their unfounded and untrue accusations and Facebook doesn't care about that either.
A few people, including myself, have reported the account as fake and for "using a name they don't use in everyday life" and they still won't do anything, despite the fact no one, not even Facebook, would say this account is using a real person's name, so it's obvious Facebook knows they are breaking at least one of their rules and they don't care.
Their advice was to block the account if we don't want to see the content! Totally missing the point that it's the rest of the world that we don't want to see the content!!