Discovery taking money they shouldn't

I have had my medical aid plan for nearly two years now. I have been debited the SAME amount every single month. Discovery took R5251 off my account instead of the normal R1954. When talking to the consultant, she said the money was taken off for Vitality that discovery "forgot" to take off for 3 months of last year and 9 months of this year. How is that possible if I have been paying the EXACT SAME amount every month. She then went on to say something isn't right with the account and the vitality team will contact me but I have STILL NOT been able to get hold of anyone????? This is not the first time Discovery has just helped themselves to the money out of my account. If it was true that they didn't charge vitality (which it is not because I have paid the correct amount EVERY SINGLE MONTH) HOW in the world can you just take a lump sum out of someone's account with NO WARNING.

I have other debit orders and bills that need to come off my account - So I need this problem rectified IMMEDIATELY!!!!!!