Cancel my application to join Discovery Bank

I was invited to join Discovery Bank, and submitted all the documentation required online. All the boxes ticked received OK, in order. Now I keep getting Emails from them, to which no reply is allowed, that I must submit outstanding documentation. This can only be done via their banking app. However, when I log in to their banking app, I get the reply that my application has already been submitted, and I should await their reply. No option to submit or any documentation. How on earth do I submit documentation to them when they make it impossible to do so? Am I dealing with adults?? If this is the level of expertise I can expect from Discovery Bank, count me out. How do I go about cancelling my application.