Messing with my credit score

I had a cellphone contract with cell c which i settled in full two years ago. I contacted them and they provided me with a settlement amount which i paid on the same day to have this settled and closed. After two years now they are affecting my credit score as my credit record shows that i owe them R29 and i am in arrers. I was trying to apply for a car but was declined due to this! I want this to be cleared and for my the credit bureau to be updated or i will be taking you to the ombudsman!