BANKING DETAILS NOT CHANGED ON TIME

I phoned Wesbank round about the 7-9 October to change my banking details for my car debit order installment, only to find out it hasnt been changed as they still debited from my old account. I phoned them on the 2nd November to make them aware and ask them to debit from my new account, the consultant who was helping me assured me that the debit order went through while I told him its impossible as that old account doesnt have money. I phoned again on the 03 November and they still emphasised it went through. I asked them to debit from the new account that day and they refused. I phoned again on the 05th because I received an sms notification from my bank about the low sufficicient money and they said they havent received any rejections. Now I received my Wesbank statement showing that there was a bounce back and they tried to debit 3 times from that old account while it was supposed to have been changed. I phoned them again today (17November), the lady helping me her name is Boitumelo told me that they dont have any proof that I phoned, I asked her to check phone records and she said they cant. Now I have to pay arrears and interest and its consultants who failed to do their job.