Double charged and refuses to give a refund

In 2016 I took out the additional insurance for my tyres and scratch and dent with Auto and general. In that time I changed my banking details with them from my fathers account to my account. The debit orders were coming off my account until my car was written off. In Jan 2019 my father realised that they had still been deducting off his account. When I phoned to query this, they admitted that they had been deducting off my account as well as my fathers account. Even though only 1 car had been registered. They acknowledged that they are aware I changed my banking details and this was not meant to happen. Then when speaking to the consultant, she said that I cannot get a refund as it is what it is. The amount was deducted for a product(even though it was deducted twice!!!!) Now this amounts to almost over R4000 over 3 years. My father did not have internet banking until recently so he was completely unaware of this. I find it pathetic and unacceptable that I cannot be refunded for this.