TransUnion Intermediate Holdings, Inc. Credit Reporting Complaint

TransUnion Intermediate Holdings, Inc. Credit reporting department,

Credit reporting company's investigation Problem with statement of dispute California

I have a 30 day late payment reported on my Transunion credit report from a company called - ( account number : - ) from -/-/2015. I personally called - and they acknowledged the mistake but said that they could n't get the credit bureaus to remove them and that I needed to contact the credit bureaus and start an investigation. I did just that. Transunion sent me a letter stating that the 30 day late payment has been verified. How is this possible when - knows it was a mistake? To me this was a lazy investigation.