Unauthorized debit order

I bought a car in Dec 2020 and took out a car insurance with one of the other insurers, their premium is a bit steep. So in April 2021, I got a quote from Discovery Insure which is R900 cheaper and the agreement was that I will cancel my other insurance and insure with Discovery Insure as from the 25th of June. On the 25th May, both insurances deducted from my account, Discovery Insure was alerted of this and they promised to reverse their debit order, as I can't from my side, it's one of those that you can't reverse. To date, they haven't refunded my money despite numerous promises to do so. According to the law I can't be insured by two insurers at once. Highly disappointed in Discovery Insure and I no longer want to switch to them. I just want my money back