Correct your link and close my account

I paid my wonga account in full only to receive a call almost a month later from Norman that I still owe R255. I told them I am not sure when I can get around to doing it, so they phoned me again the amount was R266. They sent me an sms with a link and I went on to pay it. The link said I owe R252 which I paid. I couldnt change the amount to R266 either. Now I am being told I must pay the outstanding R15 before they can close my account. And the R15 will have interest added too. 😡Absolutely ridiculous. Get your online systems in place before you send people the link.