threats of non payment of medical bills

Darned cheek by netcare parklands to threaten us with non payment of a medical bill from last year, we get a letter of final demand and they are the ones at fault as they sent thru the wrong codes to our medical aid who rejected it and were told to resubmit which they never did, so we get a final demand for payment - i sent emails to a very ****y guy in collections who told me i was wrong and that the medical aid wasnt going to pay for it and that we were laible for payment, after many more hassles i get all the accounts from medical aid which tells me once again they sent thru the wrong codes for claiming payment - and i get told to sort it out myself??? Since when has i tbeen my problem to sort out when they dont do their job properly??? What an absolute darned cheek and i dont even get any apologies ! If i had been anyone else you would have been sued for sending out false claims