Contravention of NCA

In Dec 2016 I went to Jet Canal walk to buy a cell phone on my Edgars account. At the time I owed Edgars R1 500 which was my credit limit. I settled the account and bought a cell phone to the value of R3 000. I paid another R1 500 cash deposit and the difference of R1 500 was put on my account as that was my credit limit. I continued to make monthly payments until June 2017 which at that time my account had to be paid up. I never used it again as I couldn't afford any other debt. Now all of a sudden I'm being harressed by a debt collection company stating that I owe Edgars R3 000. How is this even possible as my credit limit was only ever R1 500. I queried this with their customer care dept and was told that I appently over spent on the account. How can anyone over spend double their credit limit? Surely it is against the national credit act for any credit provider to even allow this, knowing that the original credit limit was awarded based on a customer's affordability. The answer I got was that is how it is and that I must pay the full amount. I refuse to accept this as I already paid my account. To me it seems that the company employs dishonest people as it baffles me as to what happened to the R1500 cash I paid for half of the phone. They need to get their house in order and sort out my account!