Debit Order NOT refunded

I insured a vehicle through Commrisk Insurance Brokers whom I had been dealing with for many years. The debit order for this vehicle was duplicated for the same car with a different VIN Number. This continued for approximately 10 months before I noticed it had been duplicated. I contacted my Insurance broker who after much debate informed that I would not get a full refund as somehow it was my fault? The refund due was over R10 000 and I received R2000 no explanation offered and I was told the \underwriters have agreed"to refund the equivalent of the last 4 months. """