Closing my fnb account problem!

On the 18/05/2018 I filled out forms to have my credit card closed. No contact has been made with me by fnb about the account closure. Instead I received a statement for June which states I owe R161.00. although I have since the 18 of may the day of my instruction to close the acc. not used the credit card. On the 25th of june I used fnb complaints via the internet to inform them of the problem and have since not heard from them. Although I sent instructions via fnb procedure to close the account it is being kept open and I received an SMS saying that it is regrettable that I have not paid my acc. I have no idea what to do to get my account closef