Incorrect billing

I have complained a number of times about the incorrect bill I keep receiving but Im not getting help. I don’t know who is supposed to correct this. I’m charged R500 instead of R400. Now I see the bill is sitting at R1200 yet I’ve been paying. The one time when the payment was missed the service was disconnected and I had to pay to be reconnected. I have a month to month contract so why is the service not disconnected if the payment was not received. I have even shared all proof of payments with your finance department but still the bill has not been corrected. No the wifi is not working I don’t know whether this is the cause of that but I can’t connect to the internet. I need help urgently I work from hime and Im on standby so this disruption is not acceptable. Someone please help