POOR CUSTOMER SERVICE

I have a huge problem with people who think they know law batter than us, I have sent MBD and Email requesting for my statement to make the payment as i have realized that they have tendency of increasing the initial amount to there amount, Please explain to me why it has a deference of R407? With my understanding R500 - R1743.41 = R1243.41 So how did we get to R1336.40? i called this morning at 9:45 to speak to Nhlanhla who was unsure with my request to put me through an old rude lady called Kedibone who told the Emails turn round time is 48hr yet when you ask about statement they respond with in an hour... i need a clear explanation as to how much did we get to that amount as my invoice from the shop states R1243.41, and again please STOP SEND ME EMAILS ON MY WORK EMAIL AS YOU SEE MY EMAIL ...