If you find mistakes on your credit report, you are responsible for cleaning the mess up. Recent legislation makes this easier, but the burden still falls on you.
First and foremost, you must dispute the mistake in writing to the credit bureaus which are reporting the mistake. There is no proof that you make a complaint over the phone. It's also a good idea to send the letter certified, return receipt requested.
Do not use the forms the credit bureaus provide for this purpose. Write a letter. This serves two purposes. First, you are able to explain things better in a letter. But, it additionally complicates things for the credit bureau and they're working against against a strict, federally-mandated deadline to get the issue resolved.
Once they receive your complaint in writing, they have 30 days to resolve it. They must also forward your complaint to the originating company.
If one bureau determines that they have made a mistake on your credit report, they do not have only to remove the item from your credit report with their service, they must contact the other two services with the information as well.
But, you should not count on the credit bureaus to do all the work for you. If you see a mistake on a monthly billing, you should contact the credit granting company yourself. This kind of proactive work on your part could save you endless hassles in the long run. You can contact the company through the customer service address on your bill. Again, do this in writing and keep proof.
If you can not have the mistake taken off of your record, you can write a 100 word statement explaining your side of the story.