Suspicious ********** amount on Cell C

My 3 Cell C contracts were cancelled at the end of its 2 year contract period and the numbers were ported to Telkom. During the two year period my monthly invoice for the three contracts were paid by debit order on time and never returned unpaid. After I cancelled the contracts, a statement arrived via email with an outstanding amount of R537. There was no invoice attached just an amount on the statement for R537. This amount is such an odd amount because the 3 contracts were identical at R399 each and they weren’t open lines but top up contracts so no last charges on one last invoice. The question is why haven’t they sent me an invoice and why haven’t they just debited my usual payment method (debit order). My credit profile now shows that I have not be paying my Cell C account on time with the R537 showing as unpaid. Shortly after receiving this statement (with no invoice), I received a call from their debt collection attorneys trying to collect the “outstanding” amount. They couldn’t tell me either what the amount is for. When I called 084135, they could not find any outstanding balance on my profile, odd. I asked for a paid up letter 4 times, but still nothing. This is totally unacceptable and smells like a ********** activity on my account. But the worst part is that I have tried to resolve this by reaching out to Cell C, in fact, I’ve spent several hours but to no avail. I have cellphone contracts with Vodacom and Telkom and have no problems with their customer service. Cell C has no customer service and are utterly unprofessional.