Credit card closure nightmare

I am a former FNB customer who recently changed banks. As part of the switching process I went into the Lephalale FNB branch to close my account and settle all outstanding balances. This was done on 2 July 2018. I was a private client with a cheque account, credit card account and a linked petrol card. The cheque and petrol card were closed without issue, the credit card on the other hand has been a nightmare to close. I was first alerted to fact that it was not closed in August when I was told I had an outstanding balance. I made contact with FNB and was informed that the account was not closed and that I need to send and email to get it closed (the first I had heard of this DESPITE going to the branch to close my accounts). Please bear in mind that this new out standing balance is a MONTHLY SERVICE CHARGE for an account that should be closed. I sent the email to address given and the response was that I have to pay my outstanding balance before they can close the account. Ofcourse I was not satisfied with this as I had already settled my account. In the response to my email, FNB gave me a number where I can lodge a grievance. I have called this number on more that 1 occasion and I get sent from pillar to post as no one knows how to handle this situation. Alternatively I get hung up on or get told to pay the outstanding balance which I feel I do not owe. I continue to get SMS's about by outstanding balance which is now generating interest. I have since made contact with my former private banker who has done his best to assist me. However every solution on how to pay the outstanding balance that he gives does not work. It turns out that I do not have an active card, so making the payment is more difficult. How I can have no active cards yet have an open account is a mystery to me. My wife and best friend, who are both FNB customers, have tried to pay this outstanding balance for me and every time they do they get error messages. I am annoyed, frustrated and at my wits end. I want nothing more to do with FNB yet I cannot seem to settle this payment. My last resort will be to go to branch, but that requires more hours of my time an is an exercise that has already been fruitless. FNB asks " How can we help you?", my simple answer is that they can't. Hopefully they can prove me wrong.