Account Closure Nightmare

In March 2017 I closed my Smart Cheque account & opened a Gold Cheque account. In November 2017 I received a letter informing me that my account has been handed over for collection. Prior to this, I had not received any other communication with regards to the handover, no phone calls, e-mails etc. I immediately went to my FNB branch. Simone Martin assisted me. The FNB systems where offline & she could not check, however, she promised she would call me once they were back online, she never did. So I waited a week or two & called her, she told me that she had spoken to the consultants & that my claims were untrue. I asked to speak to her manager & was referred to Ian Crimp. Ian promised to look into the matter & get back to me, he never did. I phoned him again in January & got the same story, he would look into it & get back to me, he never did. Again, I phoned him in February. He promised to look into it and get back to me that same day, he never did. Then a week later, he sends me an e-mail informing me that I should have reported the matter sooner ??? That there is nothing more FNB can do. I then got into contact with the regional manager Ian Schultz who only re**** to me after a week, then promised to hone me and is now ignoring my e-mails. Absolutely nothing has been done about this matter. No customer service whatsoever !! We are 7 months down the line. I have also logged online complaints received no response My question is, if I went to the branch twice (a debit order needed to be moved), signed all the necessary documents & confirmed with the consultant that my account was in fact closed, why was it not closed? Why am I being held liable? Why am I being threatened with legal action?