Truworths account

Please explain to me how it's possible that my account is in arrears? With 6 months to pay I owed a total of R1469, my first installment was R285 due in February and I paid R300. The second installment was R240 and I paid R300. The third R240, and I paid R400. With a balance of R469 and 3 installments left to pay according to me and the 6 months interest free agreement, I paid R169, leaving me with a balance of R300 and 2 months left to pay. I was planning to pay at the end of May, settling my bill within 5 months instead of 6 months. So now, please explain to me why I am continuously receiving calls from you guys, numerous sms's and emails stating that my account is in arrears? Is paying off debt quicker not supposed to be a good thing? Or am I mistaken? This has messed up my credit score and no matter how much you explain it to them telephonically they just don't understand. I'm seriously considering to close this account 😡