When writing the letter to the specific CRA you should include all of your current personal information.  Name, address, the current date and a copy of your credit report with a circle around which transaction you are disputing.  Never include original copies because you will not get those back.  It is very important to be specific about your claim and show as much documentation as possible.  Include copies of receipts, bank statements, or any other documentation pertaining to the transaction to show the discrepancy.  The CRA will investigate your claim within 30 days and if you supplied all of the correct information, the error should be fixed without a problem.  Any transactions that the CRA cannot verify as accurate, within those 30 days, will also be removed from your credit history.  Repairing errors on your credit report can change your credit score so it is important to know exactly what is on your credit report as frequently as possible.