THEY CANT CHANGE "DEBIT ORDER"

I'VE BEEN CALLING DSTV FOR THE PAST 3 MONTH FOR THEM TO CHANGE MY DEBIT ORDER DETAILS. I'VE SENT THEM THE DETAILS AND FORMS 3 TIMES BUT THERE STILL DEBIT THE WRONG ACC. WHAT DO I HAVE TO DO FOR THEM TO CHANGE THE DETAIL. I'VE ALSO BEEN WAITING OVER A WEEK FOR THEM TO CALL ME BACK.