Lack of service/support -unclear billing

Metrofibre attempted to debit R900, which bounced. A day later, my connection was suspended (which I understand). I immediately made a payment for the same amount. However, when I contacted their WhatsApp support, I was told I now owe R1,900. I checked all my invoices and there is no indication of where this outstanding amount comes from. When I asked for a reconciliation or breakdown, WhatsApp could not assist and referred me to another number. That number redirected me back to the original one. Calling results only in automated responses. I also tried reaching out via Facebook, but messages were repeatedly sent to my sister (the account holder) without addressing the issue. All I am asking for is a clear reconciliation explaining how the R1,900 was calculated. I work from home, and being without internet for almost two days has been extremely inconvenient. I am not willing to pay an amount that has not been explained. Please do not attempt to call us - because the last time there were lies of we tried calling and you did not answer. Kindly just send this recon so I can understand what is going on and pay what I need to pay.