Insurance not paying out sum insured as per policy

My car was hijacked in September 2015. My insurance premiums are up to date. My policy said that the sum insured is +-R177k, my renewal policy which is effective on 1 October 2015 after the hijacking said sum insured is +-R155k. Per confirmation with the insurance consultant the sum insured is the retail value however the insurance only wants to pay +-R120k as they say the incorrect codes were used when my policy was loaded. The sad thing is if I was hijacked I would have continued paying the higher premium and the fact of the matter is that I wasn't the one who gave the codes when I purchased the vehicle from the bmw dealer the bmw insurance came with it. So due to the incorrect values given to me I never took out an insurance top up.