my refund

I was just on a call with Melanie , I am appalled at the service I received her as the so called supervisor from customer service, she acknowledged that there was an oversight from your finance department but insists that I must take responsibility for your finance department's mistake. So in a nutshell, I have had this tracker account for more than three years , my insurance paid for the account last year until I cancelled it in December therefore in February I was debited R519 ( for January and February invoices). March I was debited successfully as well, TODAY I get an SMS from my bank notifying me that I was double debited for this account. So when spoke to Melanie to get an explanation for the double debit, she tells me that finance was supposed to raise an invoice but did not hence the double debit but I don't work for you guys, I don't have access to your system, all my debit orders have been going through successfully which is my responsibility as a customer to ensure that all the invoices are paid for but now how is it that without prior arrangements with me my account is debited without my consent, how does Melanie representing your company tell me that it's my responsibi