Mistakenly put my account in arrears

My cellc account was handed over to them by mistake. They had never called me, I only saw on my credit score my account was in arrears by R8000 that I wasn't even aware of, I called nimble to find out what the amount was for since I wasn't aware of it, I spoke to one of their agents and they confirmed that It was a mistake they verified with cellc and have escalated the matter to a department that will correct the error, I have since been following up with the agent that assisted me and he has been ignoring my emails and the account still appears on my credit report, my score has been affected very badly by this error, what hurts the most is that they are ignoring me.