Please can I have urgent feedback???

I recently opened an Edgars account and made a few purchases. I received my welcome letter and it stated that my maximum monthly instalment will be R850 (6 month plan). On my first purchase, the cashier was a trainee and did not include my discount vouchers when ringing up my stuff. He had to exchange my items twice and only on the 3rd time did he do it correctly. I had made a few other purchases as well after this knowing that my instalment will not exceed R850. On the 01/06/2015 I made a payment of R650 (as i was advised by Vashnee this is the amount due). I called the customer care and a lady advised me that my amount due is R1700 - R1900. When i asked how this is possible she advised me that i had purchased for R7000 - I told her that it is not possible as my limit is R5000 she argued that it is possible if their systems go down. Thereafter i sent a mail to the customer care (online) and still have not received a response. I called the customer care today to confirm if my account is up nto date and the lady tells me that i have an outstanding amount due of R1000+. I don't understand how this is possible? Edgars, please can I have urgent feedback on this matter?