Unauthorised debit out of my Cheque account!

I have been with the medical aid for years. October 2018 they debit my cheque account with my contribution and another R7,999. No notification, warning or call. I reversed the payment and since then every single month without fail this is the procedure. When I called them on the initial amount being taken I was told that it was a contribution for December 2017 that had not gone through. One whole year later, someone discovers this and merely just takes money out of my account. I have sent statements of my bank account numerous times. On the 4th of December 2017 my contribution was deducted. Another contribution payment was processed on the 15th of the same month. I reversed this payment and was then told that they sent out a mail stating they will debit our accounts 15 days earlier - NOT ACCEPTABLE to start off with. They then took another contribution on the 2nd of January 2018 which means my account was on track. I have managed to back track their statements monthly from February 2018 - September 2018 showing I am not in arrears and then in October they take over R17,000 out of my account! I have been reversing this every month and have had mails going up and down. It is totally impossible to get hold of the controller working on my account as she "cannot" take my call.

The worst part is that due to them just taking money out of my account I am paying honoring fees for my other debit orders not going through as the funds are not available and resulting in a bad record with the bank as my account is in shambles for the last 8 months due to this!