Vodacom's Billing System is Faulty and Bill for Credits as well

Can Vodacom Collections Department call me urgently. Your Billing system is faulty. You owed me R440.14 and your billing system sent me a bill that I owe you money with the exact same amount. Two days ago I paid R440.14 and I just received a statement that showed that I have a credit now of R880.28. Thus, your statement system is working but your billing system is faulty. I will probably receive another Draft Summons for R880.28 and will be again be threatened with black listing, even though your system is at fault.