Bad Credit

I had a account handed over to this firm and i made arrangments to pay off the account through KGB, once the account was paid up i received a payed up letter, however it was never updated on their side. I contacted the credit institution of which i owed but they advised that the firm never made contact with them to update on the status of my account. Currently my name is still in red under the credit bureau and its been 2 months and the status still says that i missed payments and that I'm in arears. I contacted them everyday since and have just been told that its been handed over to the relevant department. Im not sure what i Should do or contact in order to have this error corrected.