Disconnecting a contract YOU invoiced incorrectly, after confirming that all is in order

I have spoken to your office about a message received about YOU incorrectly invoicing me. The lady assured me that my account is in credit, that I do have both contracts on my account, and that I do not owe anything extra - ALL IS IN ORDER. Today, you disconnect my daughters phone. HOW IS THIS POSSIBLE? I am so fed up with MTN. Disappointed, Unhappy and So Frustrated.