Increased premiums without consent and failure to justify

I took a car insurance policy with dialdirect and agreed on a premium which by da way not even on average with the quotations I've received. 6months down da line my premium increases without my consent. I contacted them and they couldn't give me any explanation. They reversed the over charge and kept the original premium. 3 months later back to the same increased premium. Try to get reasons after no one responds. Have the sent an email cancelling the insurance, I've canceled the debit order. Now they calling me saying they willing to review my premium. Can they please continously sending me debit order mandates