diamond car insurance

Terrible customer service. Unhelpful staff. After being with Diamond for a year I received a letter from them telling me if I did not pay to renew my insurance with them they would cancel it. I had already decided to take out car insurance with a cheaper company by this point so did not respond. A month later I receive bill for £82.65 as they had "automatically" renewed my car insurance for me and covered me for a month. Surely if I take out a 12 month contract it expires after 12 months?? ...