Worst service ever!!!

Hi let me put this plain and simple. I have a sportscene account and on that account I have a credit limit of R8000. My balance was was R600 to pay then I made a purchase of R5300 online (5300+600=5900) then I made a payment of R600 to my account (5900-600=5300) then after paying my account I have credit available of R334 if (8***=2700) simple maths where is the rest of my credit I've been to sportscene, total sports and Markham. I've called customer service 4 times and online support 3 times Nobody seems to understand simple calculations. No one can tell me where the rest of my credit is. This is pathetic customer service I've not missed a single payment in the past 5 years n this is how I'm treated. Worst ever would not recommend tfg to anyone