Unfairly made to pay

On 2 March 2015, I went to the bank to settle a loan and have the account closed. Afterwards, the bank started sending me smses, threatening me with legal action if I don't pay what I still owed. I still owed??? On 1 August 2015, I went to the bank again and was made to pay R321.93. On 5 August 2015 I paid another visit only to find that yet again the account was not closed and was told I owe another R55.93. I paid that amount too. My question now is: Why was I made to pay for the bank's mistake? Standard Bank must right this wrong