If the Department of Human Services requires a provider to justify the medical necessity of a service through prior authorization, the department shall not later take the position that the services were not medically necessary, unless the retrospective review establishes that:
(1) The previous authorization was based upon misrepresentation by act or omission;
(2) The services billed were not provided; or
(3) An unexpected change occurred that rendered the prior-authorized care not medically necessary.