Increase in monthly premium

I was shocked when I saw my debit order today for my car insurance it went from R 477 per month to R 726!!! How can this be??? I did not agree to this a R 249 increase!!! I phoned Auto and General this morning they said it's the the annual increase. I have never claimed from my car insurance and have never been in a accident. They said the best they can do is R 642 per month a R 165 increase. I am not happy with this at all!!! If anything the monthly premium should decrease every year with the car value decreasing.