There are many credit tools out there, but i found the one I used was credit Versio. Instead of calling someone up and having them dispute items on your credit report, one or two items at a time, once a month, I disputed all my items and will dispute them all every month, using Credit Yersio, for 1/20 the cost. Credit Versio is 19.99 and comes with addresses to equifax and reasons for disputing each transaction and the transaction ID built in. It even emails the letter to send directly to your email address to print out.
However if you don't want to use Credit Versio or any other app, the address for Transunion is P.O. Box 1000, Chester, PA 19022 and the address for Equifax is P.O. Box 740256, Atlanta, GA 30374-0256 and the address for Experian is P.O. Box 4500, Allen, TX 75013. Send them the details of the transaction and why you want to dispute it, or all the transactions and why you want to dispute them, and repeat until your credit is better.