Cancellation of car insurance

Why is it so difficult to get a policy cancelled? I called on the 22nd, and after a lengthy telephone conversation was told I would be called back. Instead I receive updated policy documents for a policy I cancelled. I called AGAIN on the 23rd, again was transferred to the retentions consultant and I refused to repeat the days before conversation, I only wanted my policy cancelled as I have sold the car. The consultant confirmed it was done and I would get a cancellation letter. I have not received one and it looks like I must call AGAIN tomorrow and possibly stay on the line until it is done and I receive the confirmation. I would certainly not refer anyone to Outsurance as this type of service is poor and dissapointing.