Frustration with changing account details

Despite numerous attempts to change banking details for my two accounts (mobile and data) I simply get an SMS notification that it is not possible. This is insane! I have been into the store, I have called your call centre, I have emailed, I have had a return call from a call centre agent confirming all the details. And then a SMS informing me that it is not possible and to call the call centre AGAIN. Which I have done - and hung up after 20min of no response other than being told multiple other ways to address my problem by a voice recording! This level of inconsideration for a customer's time to get her affairs in order so that you can get your money every month is ridiculous. I expect a phone call on my personal number to resolve this urgently.