We are starting to see a lot of questions like yours. Since you prepared your tax return and filed before the tax law changed for the tax on unemployment, you owed tax due and then learned you should not owe so much or might even get a refund---so you did not pay your tax due by the May 17 deadline. Now the IRS computers are churning out notices to people who did not pay their tax due.
Eventually---sometime during the summer--- the IRS will recalculate the amounts of tax due or refunds for people whose returns were filed before the law changed----but it may take a few more months.
Call the number on the notice you received from the IRS----it will probably be hard to get through---but be tenacious.