The payment may not be registered with their billing department in time to stop the DD.
If your payment takes a few days to filter through, and they prepare the DDs in advance to send to the bank in time to be processed on the correct date,given the snails pace that the banking system works at, 10 days may not be enough.
Can you cancel the Direct Debit ? So long as its active it can still potentially be abused regardless of your account balance with any company as far as I know.
You can pay your Board Gáis electricy bill via your own bank, the post office or billpay.ie BUT you will pay more because if you pay by direct debit you get a better rate, your rate includes a 2% Direct Debit discount.