Discovery Insure Cancellation Issue

I have been trying to cancel my Insurance Policy for a week now. My car is already sold and not with me anymore, but Discovery still hasn't responded to my emails (I've sent multiple to multiple email addresses). When I phone in (which I have been for 5 times already) each time I go through the whole process until I get to the cancellation department to confirm my ID number and then the phone gets put down. I am tired of struggling now and just want the policy to be cancelled and the remaining period of the month to be refunded (which was already paid for in advance).