FNB worst service confused people

I am so fed up with this bank. I have been with them for so many years. I just found out that in 2011 my pension and provident fund was put into my account. At that time I did not close the account it was active. Now this FNB says that they cannot find details of the account as they delete all info over 5 years. They even refuse to give me a statement. The branch have the most confused people alive... They know absolutely nothing. They said that the money was used as service fees when they closed the account.. i did not receive the money's. Now I need access to the account. If FNB does not either pay me back that money or give me access to the account I will be forced to open ******** charges of theft against them as they took my money without my permission.