Why wait for confirmation of non reverse of debit order if account was paid up in full before debit order went through.

Settled my account in full with them in the prescribed timeframe, but still a debit order went off. When querying this I get told that they need confirmation that the debit order is not going to be reverse. the more I explain that the debit order should not have gone off at all due to full payment of the amount owed, the more I get the same answer. Eventually I get told that after 10 days I should enquire again. It has now been 12 working days and I still get told they need confirmation that the debit order will not be reversed. I got a statement that shows my account is owing me money but they refuse to answer me as to when this will be paid out to me. I want my refund now!