Standard Back cannot follow simple instructions!!

Standard Bank must be the most useless of them all. I have Vehicle Asset Finance with them. I called very early in the month (March) and advised them that I want to change my banking details that they debit my instalment from. I was assisted by a Mr Nathaniel McMaster. He assured me that he had processed my request. He then requested that I send an e-mail with the proof of my new account. This e-mail I sent directly to him on 7 March. Today I receive a call from a lady called Busisiwe Tshabalala from MacRobert Incorporated. Apparently I am in arrears with by vehicle account. I explained that I had changed my debit order banking details and how was it my fault that Standard Bank did not follow my instructions. She continued to argue with me saying that it was my responsibility to now pay this account. What I don't understand is whose fault is it that the bank cannot follow simple instructions and secondly I am handed over to attorneys by this bank when they failed to make the debit order. Absolutely ridiculous!!!! Its like one is being punished for being a good paying customer!!