They keep your details when they shouldn't

I needed to change me ID number and was advised to close my account and open another one. The problem is that they keep your cell number in their system so you cannot open another account. Since January I have been trying to get them to delete my contact number from their system, but they tell me they can't. I am still getting messages that I havent used my bank account even though it is closed. So if you change your contact number you will have problems. Will stick with the major banks.