Astronomical jump in premiums

Dont be fooled by auto and generals initial premiums when you join them, they paint a pretty picture to get you to join them, then after a year of being with them they have increased my premiums astronomically by more than 70% with no reasoning behind this, the only answer they can give me is that it's a brand review, ive had no claims in the past, being a customer with them, so why should my premiums go up . Surely when a vehicles retail value decreaes, so should the premiums?? Shocking that there is no explanation for this from the call centre only that this is a brand review. day light *******!!!