Excessive and unexplained premium increase

My car insurance premium has just gone up 12.5%. Discovery have a long explanation, none of which I feel is applicable. I have made no claims, inflation is closer to 5%, the exchange rate actually improved over the period, and of course vehicles depreciate. On top of this, they are hiking the rate less than 12 months after I insured the vehicle. I complained and they just emailed back the same standard reasons which don’t add up. They seemed very keen to gain my business earlier this year and I thought I was a valuable customer – clearly not.