VERY UNHAPPY

I am VERY UNHAPPY with how much account was handled by Acquifin. I'm expected to just accept that "mistakes happen" and pay!! I spoke to Omphemetse on November 30th and she informed me that I owe R1370 (the call was followed by an SMS confirming the conversation). I paid it in 2 instalments in December and provided proof. Today I was informed that I still owe them and that the R1370 was a "mistake"! TOTALLY UNACCEPTABLE as I am expected to pay this by 31 January (in 8 days), and they're telling me as if they're doing me a favour, as if their system malfunction is my fault