Cell C unfair treatment

In December I requested settlement amount that I need to pay in order to close my account and they gave me, and I paid that amount in full and requested to have the account closed and they said the account is closed but now I received calls from debt collectors telling me that my account for cell c was handed over for collections, the amount owed is was R140 they said but now since it's handed over I needed to pay R420.39 to have that account closed which includes collection fees for lawyers, my question is why did Cell C say the account is closed when it was not? And why did they not contact me directly and tell me that the account is outstanding instead of handing my account over for R140 and costing me to pay R420.39 because of collection fees.