Bad communication

I Lost my card and had to phone in from a store to report the card - they made me feel like a ******** and asked my questions I could not immediately answer. I am not a regular shopper at Old Khaki and could not remember off hand when my last purchase was or when I made the last payment. I never shopped there again. I used to receive invoices through post but it stopped in June 2015. I received 2 electronic statements after that (August and October). I could not believe there is still an outstanding balance and phoned them on 15 December to request a Invoice to see the details there off. The lady mailed me the statement (dated 12 Nov 2015). The Closing balance was R140.00 which I payed a few days later. Never heard from them again until last week when I received a sms - with a link to an invoice this time - indicating I owe them R270.00. After another phone call an my account, they inform me that I had to specify that I wanted a settlement amount. This is the only clothing account I have that charge a basic admin fee of R50/mnth above the interest. They refuse to reverse the charges and imply I have to pay R270 without them doing any admin for months or me buying anything