Dishonesty in car insurance

In Nov 2021 my car retail value was said to be Approximately R 279 000 on the policy document. Throughout the policy life cycle since 2013 the vehicle has not been below that amount. I have also been paying premiums aligned to the value of the car. On 10 Dec 2021 I was involved in an accident and the assessor wrote the car off. When I go through the claims process I was informed the vehicle is valued at approximately R 182 000. That is a huge depreciation in a space of 10 days. When I challenge this I am informed I will get a rebate for the unwarranted high premium I have been paying all along. This is not acceptable and I feel the company has been dishonest. Please remediate asap as I currently don’t have a car.