Unauthorised debits from my account.

I took a motorvehicle insurance policy with outsurance. During the cooling off period I decided against the insurance, called them and told them I have decided to cancel. I even sent them an email of cancellation. They sent me an email of proof that the policy is cancelled. The agreed monthly premiun would be R1040 for two vehicles and to start cover on 01/01/2018. To my surprise, they keep on debiting from my bank account even after several attempts to warn them. In total +/- 3500 has been taken by them from my account in one month as insurance premium. Every time I have to go to the bank to reverse the withdrawals. My account ended up being negative which made my profile poor with my banking institution. I calle Outsurance almost every now and then, but nobody is prepared to take responsibility.