Vodacom Poor Billing System/Department

I logged a query with vodacom regarding their billing system. They billed me for a device which they also dont know off. I reversed the payment in March and paid R2080 in April to settle the amount which was due. But they still say my account is still outstanding after paying the amount. Contacted Vodacom numerous times and their billing consultants are failing me. Im paying for 3 lines and right now my line is due for an upgrade but I have lost hope and trust in Vodacom and think of cancelling all lines. Your Vodacom account is in arrears. Payment of R2361.55 is urgently required to avoid service interruption. Please call or SMS*** to arrange payment.