Changing account detail

I have been overseas for a couple of months and my cell phone number on record with Standard Bank has been reassigned to a new user, since I did not use my phone overseas. When I realized this, I emailed the bank to remove this number from my profile as I thought this could threaten the security of my accounts. I have finally given up today. They cannot do this. At first, I emailed ********** After no response, I mailed them asking for any feedback. A couple of times they came back to me to ask to provide information. I copied and pasted my original request and pasted it onto the response. This happened about a couple of times. A couple of times, they advised that I should go in to a branch to update my information. I told them that I am overseas and that I could not go to a branch. Finally, they advised that my request would be forwarded to Prestige Banking. I asked them not to, because the service at Prestige Banking has been even worse in the past. I moved my current account from Standard Bank because of it. It seems that it was anyway passed on to Prestige Banking. Once again information was requested. Once again I copied and pasted my previous info on the response. I once again asked for feedback repeatedly. Finally, they came back to me and advised me that I must please go to a branch to update my information. I do not want to add new information to my account, because I understand that that could be a security risk. The email address I used is the one they have on record. I cannot get this right. I have given up. I have managed to change my information with my new bank and my insurance companies doing it this way.