FNB accumulating fees after bank account was closed

Good day

Yesterday I received a notification SMS that SARS had made a payment into my FNB account. I went to the bank to see if I would be able to withdraw the money because I closed the account. To my surprise the account was never closed and I now have tho pay R5000 for monthly fees that accumulated. The lady that assisted me says that she can see that I closed the bank account but there is nothing they can do and I am liable for the costs. I had to pay R200 at the tellers the day that I closed my account but the R200 went missing and the account was never closed. My contact details stayed the same and I was never contacted to say that my account is running in arrears with monthly fees. Although the account is dormant I am paying a higher fee than normal. Please assist with this matter, I feel that I can not be held responsible for errors that was out of my control.