MTN Customer Care Turned My Final Statement into a Mess

I migrated my contract to pre-paid last month and received a final statement - over 700 odd Rand payable on 13 Oct - that showed invoices, but not payments and there is something wrong. Customer Care and Retentions have no record of me, because I'm now on pre-paid. I was told to go to an MTN store, which I did. The consultant e-mailed customer care and I was requested to provide my details which I did. Still no reply. Now I receive an invoice from <no reply> that I allegedly haven't pay an amount of just over 400 Rand. It's such a mess and no communication, making the customer run from pillar to post. Accounts Department fix this!