Notice of deficiency

California.
The IRS says I owe them money, most of which I have already paid. They insist that I never paid them 1/3 of what I did, I have the returned checks to prove otherwise. I've sent them a letter explaining that I had already paid them, but it's like they can't read or something. Now they're telling me how I'm being charged interest and late fees for something that I already paid for. I have since sent a letter to them with copies of the checks that I paid them with.

I'm not too sure they'll understand this time either, what should I do?

The Taxpayer Advocate Service is a service of the IRS. The Taxpayer Advocate Service can help you if you have tried unsuccessfully to resolve a problem with the IRS. Your local Taxpayer Advocate can offer you special help if you have a significant hardship as a result of a tax problem. For more information, call toll free 1–877–777–4778 (1–800–829–4059 for TTY/TDD) or write to the Taxpayer Advocate at the IRS office that last contacted you.