I want my banking details to be amended & not getting any assistance from this bank

What a pathetic service ! I Called this call centre because I want my banking details amended ...i called the call centre on ***since the beginning of this month till to date I have never received any assistance...I spoke to an Agent who confirmed that they will return my call ..till to date nothing has transpired secondly your call centre number takes forever to be answered ... today I called again I spoke to Swazi who confirmed that an Agent will call me ..till now I'm waiting for a call...how long should I wait for a call or for someone who will assist me on amending my banking details ...like how long ..a month ...6 months or a year ????? because I need to close my account and I want my account details amended