*********** invoicing with no remorse

we have a few contracts with telkom, they submit us invoices and have never once done a debit order. we've always paid via easy pay. in January an invoice was submitted to us, saying after all payments, we are liable for an amount of R491.04 was due on the 29th of february 2024 we generally pay more than the amount due on the account, always rounding of the total. we didnt question it as it showed the deduction breakdown on the invoice. still we paid an amount of R1050. Suddenly debt collectors start emailing us requesting payment, spoke to Bruce, he said it was an error on telkoms end and they will rectify, and now suddenly we disconnected and an amount of R1900 is being requested to reconnect our services!!!!! I don't have that laying around! what happens next? Am i to be bul**** to pay up due to an error on their end?? Their *********** staff is no help.