UNFAIR TREATMENT BY FNB

I am so disappointed with the treatment I have received from FNB. I opened a cheque account with FNB due to their high bank charges on the account I switched banks. Then I called the call center to instruct them to close the account. But the call center agent advised me that the account will be closed automatically due to non activity. I left it at that taking her word for it. To my surprise today I received a call from CBS Legal advising me that I owe R7020.98. To my disbelief I went to the branch to inquire, they confirmed that the account was indeed handed over to CBS Legal and the amount was because of monthly charges that accumulated over the months. How can I be charged this ridiculous amount for a service that I have not used ? Is that fair FNB? When I was mislead by one of your agents....