Debited account without permission to do so

I have vehicle finance through Absa and last month they deducted +- R600 additional to my monthly payment, when I went into the bank to find out why, they told me it was because I didn't have vehicle insurance, I explained to them that I have had insurance with Dial Direct for the past 2 years since I've had my car. I needed to send them proof of this and I have done so. Now AGAIN they have deducted the +-R600 additional to my monthly payment after I have sent the proof through to them. I have demanded my refund and I am still waiting for this to get sorted out. I don't understand where they received permission from to debit my account as I have not been contacted by them at all