My line was put on hold due to an “unpaid amount

My line was put on hold due to an “unpaid amount.” However, I had already made payment for June and received my July bill. I understand that I upgraded my phone and incurred a residual device charge. After speaking with the Telkom agent and confirming my request, I wanted to have the remaining fee paid in instalments. Unfortunately, my July invoice indicated otherwise and is ready to debit the full amount. According to Telkom, the reason for my line termination is that I owe a R600 amount that was not communicated and is not included on the invoice. This outstanding balance is the reason why my bill is being terminated. I will not pay this amount within the 10-day window because my line was terminated today. This would not only result in me paying the invoice amount but also an additional R600 that will not be refunded on my account. At this point, I feel as though Telkom is taking advantage of its customers due to the incompetence of its agents.