Hi @michaelmom,
You're absolutely correct about worked to dispute the inaccuracy in your credit summary. Because TransUnion controls the content of your credit report, they are the best ones to help you resolve. You mentioned that you already reached out to them in writing, but here's a link to their Contact Us page that provides some additional options to reach out to them.
Are you already using a service or platform to track your credit score?
There are a number of free options and that can help you stay close to your credit score and hopefully help you see the improvement once the credit inaccuracy is removed.