Premium change 35%

I got an email from Hollard stating that my premiums will be adjusted by an increase of 35% yet the insured value of my car has dropped. I called them to find out how do they come up with this calculation and the lady from the call centre said that is because of storage costs and supplier costs and I have a choice to cancel my insurance if I want but that is how it is. They also said it is based on my driving and usage of the car but thy never contacted me or anyone who would know how and when I drive my car, yet they made a decision using that information? A 35% increase in premiums with a lower value insured - ridiculous! The call centre individual that took my call basically told me you can cancel the insurance if you want, but this new premium is what it is.