Incorrect billing for over two years

I have been contacting discovery for a while now advicing them that they are billing us incorrectly .this is going on for over two years . On the keycare plus option , the charges should be R330 for the main member and R330 for his child . All are family members are helping him to pay this medical aid because he was incarcerated since July 2013. I have sent them letters from the officials and a consent form . This morning when I called the lady to resolve this query , she tells me that they have changed the policy two months ago and this option is only for the main member and not for the members dependents. I printed the 2015 pricing and it states nothing of this sort. They owe us a refund and now they being rude .When I questioned the lady at customer care this morning at around ten o clock , she was rude to me and cut the call . I am a member of discovery for many years now and I don't like being treated like this . My membership number is *** and my sons is ***. I really would like a response as soon as possible