Cell C , poor customer service

Had a cell phone contract about 6 years ago, went into store to settle the balance due and cancelled contract. Last year cell c listed an adverse on my name and I have never been informed that there was an amount outstanding and my personal email address has remained the same for them to get in contact. I only found out about the adverse as I work for a bank. This is affecting me negatively especially at work. I tried calling the call centre, they referred to their attorneys. I called the attorneys twice and in store and they say they have no records of this. This is becoming so frustrating as it is something that is not getting resolved.