Taking more without consent. Greedy company!

I recently bought a vehicle and have taken insurance as required upon purchase. However, for reasons unknown and not agreed to MFC via Nedbank don't acknowledge my existing insurance and feel they need to take more money from me for insurance on the vehicle. So now I'm forced to pay 2 insurances on 1 vehicle. This all done without my consent and when you send them proof of insurance they still persist to deduct more money from me without reason. I am terribly disappointed and inconvenienced by such blatant lack of professionalism by an organisation that should know better.