The IRS says I owe 10026 in taxes from 2021, but they have my income as higher than I actually made. Stocks sold were counted in my w2 and also by the IRS. What can I do?

My previous employer counted my stocks sold as income on my W2 in addition to the income I made working there. But the IRS is also counting those stocks as additional income, so it looks like I made twice as much money as I actually did.