Except as provided in subsection (c) of this section, a carrier may not increase an individual’s premium on an individual health benefit plan more frequently than once every 12 months. An increase in an individual’s premium described in subsection (a) of this section includes an increase due to the individual moving into a higher age band. A carrier may increase an individual’s premium on an individual health benefit plan more frequently than once every 12 months if the premium increase is due solely to the enrollment of a new family member to the individual health benefit plan of the individual.