Most *********** account management in South Africa

I received an incorrect SMS on the 7th of February, saying my account is in arrears and has been handed over for legal action. After spending hours on the phone that day and getting confirmation that my account was up to date, I cancelled, since I don't take kindly to threats due to incompetence. Today, almost 6 months later, I get another SMS from them saying that my account is in arrears and I need to urgently pay it to avoid being handed over for legal action. Can someone please explain to me how it is possible that an account that was up to date when I cancelled it, is now suddenly in arrears after 6 months?