Complete non-response and inflexibility

I live in New Zealand and have an ABSA account through which I pay my continuing SA policies and other expenses. ABSA has a dated mobile number on their system. This means that I am unable to set up new payees (or any personal detail changes) since the authorisation code is sent to the old number. I tried to change this two years ago to only receive an incorrect reply (and when I tried to point this out in a subsequent email I was simply ignored). Since I could still transfer funds into the account to cover my monthly payments, I then just left it. However, with a large amount of money potentially flowing in from a matured policy I would like to be able to transfer funds from this account in future (as is my right). Thus I tried again: I phoned ABSA international number but gave up after ten minutes since I was paying international mobile rates. I wrote to them again and now, three weeks later, have received absolutely no reply. ABSA are the worst bank I have ever had to deal with - and what I have shared is only the latest of a very long list of bad and upsetting service experiences. All I need is to change the mobile number they have on the system or, at least, to have them change the destination my authorisation code to be sent to my email address (which they already have in their system so would only involve a click of a button). I am unable to change any of this myself since each change requires me to receive a code which - you guessed it - is sent to the wrong number. So, yes, I am well and truly left stuck since I am dealing with a bank that simply ignores its customers - even when it comes to their right to access and manage their own money.