Journal unsatisfied with revisions after acceptance, author proofs and copyright
Unfortunately, these things do happen sometimes, and there's not much you can do about it.  If the journal does not want to publish your paper yet, there's not much you can do to get it to publish your paper without carrying out the revisions that they request.  At least they caught their mistake before it was actually published, unlike in this case at PLOS ONE, so you don't have a retraction on your record.

I would suggest you treat this just as any other request for revision: improve the paper and hope that the next revision is sufficient for publication.