Unauthorized debit orders

Their account department service nowadays is very bad, debiting R2500 (25 Aug-1059, 27 Aug and today R399) for a debit order of R399 per months, when u call them they say wait for 14 days for refund while waiting for they debit, one of their call centre agent advice me to reverse it from the bank while they knw it's not reversible, can someone please help or advice, I can't change the acc coz debt order has to go through.