Debit order went off despite cancelling policy

I cancelled my building insurance policy last month (about 10 days before the end of the month). I was assured that the policy had been cancelled and that it would not go off this month. I requested a confirmation email but this was not sent - I didn't have airtime to call back so I trusted that all was in order. Yesterday, the debit order goes off, bounced back as I had insufficient funds (I did not budget for this to go off as I'd been assured it was cancelled), so I get charged a fee for the debit order bouncing. THIS IS UNACCEPTABLE THAT THE POLICY WAS NOT CANCELLED AS CONFIRMED BY THE AGENT!!!! I demand someone call me immediately and correct this as well as reimburse me for the airtime I used and the fee charged by my bank for the debit order bouncing.