Bad service

Hi. I visited FNB on the 5 February 2010 to request for proof of banking details to provide to City of Tswane. I have recently discovered that the account number is not mine as I had completed some work and was expecting payment. When i queried with City of Tswane they showed me the proof of banking details and the account number was not mine. I visited the branch and they say its not their fault but it is Matshediso Mahlangu's fault and that because she no longer works there there is nothing they can do to assist me with. I want my money back.