I cannot do so Wesbank will not assist

I have tried to change my debit order details, and Wesbank thinks I have sold the vehicle, I have explained numerous occasions that the vehicle is not sold someone else is now taking over payments. And they just don't understand. why cant I change my bank details it is not a crime, The instalments are up to date and not in arrears.Pathetic service . The vehicle will remain on my name, SO WHAT IS THE PROBLEM, Wont do business with Wesbank ever again in my life as there is no service.