False Advertising and Non-payment of Hospital fees

my Child was admitted to Private hospital on the 09/08/2017. we've never had any issues with regards to the medical aid. now I received a bill of over R 6000 for hospital and another 2500 scans requested by the doctors, for which the medical aid does not pay. there is no reasons given as to why? previously when he was admitted there was no problems or co payments. none of this was mentioned to me. so this surely is false advertising of Unlimited private hospital coverage as per the website. the hospital was on the list to use. so why is there all of a sudden bills? my wife needs to go for a c-section on the 16th of September which she has already received pre-authorization, however we are now scared there will be more bills coming? why have a medical aid if you almost need to fit the bill?