Refund

I took up a contract with Incredible connection and increased my installments to pay up quick. So my debit amount had been R1000. On the 22nd of November I requested my settlement amount which I got it was R1191. 53 That was after my debit order for November had already gone off on the 20th of November. On the 22nd of November I made a payment of R691.53. Which according to my calculation I was only left with R500 (exclusive of fees) for month of December.

December 13,debit order went off of exactly R1000, which is understandable, but I was expecting a refund of the difference of R1000-R731. 45(which is remaining balance of R500+fees) however according to incredibly connect finance department, they don't owe me. I was communicating with Themba and he is failing to make me understand what happened to my R268. 55.

I need to understand how? This is basic maths.