Massmart Health Plan no cancellation policy?

How is it humanly possible not to be able to cancel your medical aid for your dependants i.e spouse and kids if you are unhappy with your medical aid? How can Masssmart Medical Health Plan administered by Universal, inform you that you can only cancel once your kids turn 18?

The service we have received is absolutely pathetic, none of my child's medicine is covered, call centre agents tell you you must change it, only cover R550 of specialists fees plus when I called the call centre to inquire if we can go to the Netcare Emergency section due to a tight chest they said yes but lo and behold we were not covered. When you add all of this we spend over R4000 per month on medical expenses that this medical aid doesnt cover the medicine and specialist fees and therefore decided its too expensive to be on this medical aid.

Why in heavens name are we not allowed yo cancel? I need to make contact with the Ombuds next.