wrongfull judgement and bad itc

I was contacted on the 5th of June via sms regarding an outstanding account with HiFi-corporation. I told them it cant be cause I paid the account in full 2 years ago. Several times the phone was just put down in my hear. I went to Hifi corp in cape gate phone head office at hifi finance they confirmed it was a mistake and sent me a confirmation email that the account was settled. I faxed this to ARA group they refused to assit me to remove the bad credit rating on my itc. It wasn't my fault phoned them several times they refuse to assit me and said it wil take time to repair my credit scoring this is unacceptable they are unprofessional and I wil make a legal case against them. Because of their mistake and refusal to repair the damage done to my name I cant make debt or other investments because my credit score is low.