Ok well the first step for you is to contact the company's accounting/payroll department and tell them about this situation. If there are in fact wages that are due to you as a result of your employment with them such as commissions earned, bonuses or other income earned you were unaware of, you need to make sure they re-issue those checks to you.
You will need to contact your employer before you respond to the IRS because it may be a payroll error within the company where they have an active employee who is being paid but they are still filing 1099's to the IRS under your social security number. If this is the situation, the company can fix the error and then issue you a letter so you can send this to the IRS and have your case closed out.
If you are unable to resolve the situation with your company then you will have to call the IRS number on the file and dispute this situation. The good news is that by tax regulation, you DO NOT have to pay taxes on income you never received. However, you will still need to present your case to the IRS. It shouldn't be too difficult to prove that you didn't receive income, you will just have to send them a copy of your bank statement showing that there were no direct deposits from the company, no cashed checks, no deposits in the amount of your wages, etc during the tax years in question.
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