OUTsurance credit shortfall additional excess

My family including myself have been insured by OUTsurance for more than 13 years with only 1 previous claim for a windscreen in all that time. My father has been receiving OUTbonusses for more than a decade and has never missed a premium. Last week my mom drove my vehicle which is on my fathers policy and a truck driver due to negligence wrote off my car. Luckily my mom did not get hurt too badly and naturally we logged a claim with OUTsurance. We have comprehensive cover on the vehicle and credit shortfall and we expected to pay only one excess of around +-4000 which was the supposed basic excess. OUTsurance than said we owe them an additional amount of around +- 4000 as an additional excess for credit shortfall. I have never heard of such an excess and my father also claims this excess was never mentioned during the sales call. So now we need to pay over R8000 to get my car paid out which is ridiculous. OUTsurance creates a binding contract over the phone but their scripting does not fully disclose all their Terms and Conditions to their clients. I have lost a lot of respect for this company and have advised my father to start looking for another insurer because if OUTsurance can do this to us who have a near perfect insurance profile with them and have done business with them for nearly 2 decades then they can do it to anybody. I am extremely disappointed and disturbed by a company who claims to have no additional excesses charging us this additional excess especially considering our profile and claims record with them...