Overdue account for non existent service

My adsl had numerous problems and after complaining about the fact i shouldn't be paying for an non existent service i received the following sms. From: +***<br> Received: Mar 20, 2015 12:07<br> <br> Good day<br> <br> Confirmation that credit has been passed for ADSL and data services, your current outstanding balance is R563.80, due on the 7th of April 2015.<br> <br> Kind regards<br> Telkom Online<br> <br> i paid R600 on the 1st of April but i received a statement that my account is R256.99 overdue.Please sort this matter out urgently as it creates a negative image on my account when i am not at fault.<br>