I could not sell my mutual fund. The agent told me the IRS put a C Notice on my account. I filed the 1099-DIV on my 2018 returns. How can I get my money back?

I want to get the full amount without any withholding so I can reinvest this year. I have had no back taxes from previous years. I've filed every year and paid off any tax due. How can I get the IRS to remove the C Notice on my account?