Trouble with car insurance cancellation

I have been struggling since the 2nd of September to cancel my car insurance with A&G. As per The Agent (Name unclear) I have to give reasons for my cancellation. Though I have given them reason, they are insisting on me giving them proof substantiating my reason. I find this rather puzzling as I don't have to go into my personal reasons or proof otherwise. What I am asking from them is a refund for the month of September as I haven't been using the car since then. The same way they didn't require a reason or "proof" when I took the insurance, they should refund me