Unauthorised dedection of R6648.50 from my bank account

Lake Smit and Partners in Gateway Medical Centre has been ********ly deducting R6648.50 from my bank account. I only authorised them to deduct the amount on 25 September but they never stopped debiting my account on 25 October and 25 November 2019. I had to call them each time to refund my account. I've asked my bank to stop the debit order but they are not the most efficient bank as well - they haven't done it. Now Lake Smit is not responding to my e-mails. I'm a single parent this is a lot of money to me. I just want them to refund me and stop the debit order.