Substitute for Return

I own a small business and haven't filed my returns for the last 4 years and the IRS is sending me a bill stating I owe taxes during that period of time. How can this be and how do I fix it?

Likely what has happened is that the IRS has discovered you had income that was unreported and they filed a return on your behalf. This is called a Substitute for Return(SFR) and probably includes penalties for failing to file on time. When a SFR is filed it is done so in the best interest of the US Treasury filing as Single with standard deductions. If a SFR is filed and there is liability the IRS will assess the balance and pursue collection. If a refund is due the IRS will leave it as unfiled. The unfiled returns can be filed and the SFR corrected which may reduce your tax liability. However it is unlikely any penalties will be reduced or eliminated unless you can provide reasonable cause for failing to file such as a hardship or unusual circumstance beyond your control.