Poor Service and Threats

This amounts nothing but harassment. A few months ago I open an FNB credit card and was offered a Cheque card which I took at a spur of the moment, however shortly after that I called in to request for the closure of the account and it hasn’t been done three to four months down the line. The reason for the request was that I work for another bank and it does not make sense to have another cheque account. Lately I’ve been getting messages and threats from FNB that they will affect my credit rating because of this. What did I do to deserve this? Why can’t they just keep their promise and close this account? Because now, it has run fees and charges and I requested for the closure of the account long before that.