Double deductions

I agreed on a debit order on the 20th of each month but every second month the debit again on the last day of the month. This has been going on for a while and I call them to rectify this mistake as it messes my credit record for unpaid debits. I have sent them my bank statements as they requested them in order to pay the bank charges I have been incurring but none of them ever gets back to me promise after promise. Called them again this morning after waiting for their call at 9 am which did not happen. The gentleman I spoke to said that they will only refund me on the 11 of May. the question is why should I be calling them every time for the same mistake and they don't seem to care, why am I the one that needs to be inconvenienced all the time. <br> <br> Millicent was the only one who called me back after speaking to their finance department who according to her were to get back to me.