Debit order date never changed

During the month of Sep 2017 I had requested that my debit order date be changed. The vehicle was then traded in in October, dealer then settled the amount but because Wesbank had never changed the debit date as requested the dealer settled less one amount. I have proof that dates were requested to be changed. I will not settle this amount due to Wesbank's negligence!!! If the job was done correctly in the first place the dealer would have settled the full amount outstanding!!. Oh and lets not mention the pathetic service you receive...