CellC owes me money yet CSS tries to collect on a closed account

I am so ****ing over this! Months of harrasment between CSS and CellC over an account that CellC owes me money on... I over-paid by R100, on my ITC record is shows "account closed" yet I am still getting calls and "threats" from CSS. When they ask me to send proof that it's paid up and I send them the account showing that CellC in fact owes me money, I don't get a response. 3 weeks later I get threatened via SMS, email or call again... This has to stop. If this continues I will publicity tag and post the conversations on every social media outlet I can find that either company remotely has a connection with. It's pathetic!