Gap cover issues

Discovery suspended my gap cover and supplementary gap cover without informing me timeously that they didn't receive the premium. This was not a fault on my part or my bank - they confirmed there is no stop order on Discovery's debit order. Therefore, it was Discovery's fault for not collecting the premium - they said they had a technical difficulty. However this has happened more than once. The first time I complained and they said I should either pay the premium into their account or they can deduct it. Since it's a debit order I said they should deduct it. I thought it was sorted but now it happened again. Quite frustrating.