Debit order cancellation nightmare

I recently sold my car and contacted them 1 week before the debit date to cancel. I was told someone from retentions would call me by 14:30. Didn't happen, called again the next day was told that someone would call me and again nothing. 3rd day called and requested to speak to retentions, cancelled the insurance and was told no benefits would be active from that call onwards. I agreed and they said they would cancel the debit order. End of the month comes and they debit me, I have sent 2 emails since and no communication at all... This to try cancel imagine if I had to claim.......