Unfair customer treatment

I have had a contract with MTN since January of this year, and I have not missed any of my payments. However, in August, it was reported to credit reference agencies that I had missed a payment. I contacted the call center, and the advisors confirmed that there are no missed payments on my account. Unfortunately, they were unaware of which department would handle my query, and my calls were eventually dropped. I have made several calls, as this issue has negatively impacted my credit file.