Refusing to cancel my policy

I had been with King Price for over 4 years insuring my car. I sold my car and want to cancel my policy, but it seems impossible to do so. I keep on phoning them and each time they try selling me new insurance because they don't want to loose me as a customer apparently. Each time I tell them that I am not interested and just want my policy cancelled whereupon they assure me that they have cancelled it. I however have no confidence in the senior consultants I speak with every time and therefore I keep on phoning them back every day to make sure that they have indeed cancelled my policy. However, each time they tell me that my policy is still active and that they promise me that they will cancel it, but only after trying to sell me more insurance policies. It has been more than a week already and my policy is still not cancelled. All I want is to cancel my policy! The service that I have been getting from King Price has resulted in me never to consider taking any products from them again in the future and will not recommend them to anybody I know.