You're not being taxed "for filing bankruptcy". You're being told you owe taxes that you didn't pay and that weren't discharged in your bankruptcy case. Pay the tax or see a competent CPA or tax attorney.
You are certainly confused. There is no tax for filing a bankruptcy case. You got a bill for income taxes (or related fees or interest, or possibly employment taxes). The IRS can, and will, go back several years to send you bills for unpaid taxes. See a CPA or tax accountant.
You are not taxed for filing bankruptcy. You can be taxed on debt forgiveness, but not for debt discharged in bankruptcy. Some of your creditors may have reported debt forgiveness before or after your discharge. You'll likely need a tax professional (and I don't mean a tax store) to help you. I'd recommend a CPA or Tax Attorney.
I recommend reading the documents you received closely. A client of mine recently received the same letter you probably did. On the 4th or 5th page the IRS tells you to send a copy of your discharge to them, and to tell them you don't owe the tax b/c you filed bankruptcy. See a tax professional to see if you should also file IRS form 982, as well.
This is not to be construed as legal advice, please consult a lawyer regarding important legal decisions.
To answer your question, I would first review your original bankruptcy petition. I think your question is confusing, but my answer assumes it is an income tax liability that was owed at the time of your bankruptcy fiilng. Review it. If is for a tax older than 3 years from the time of filing, they may or may not be discharged. Also, if the tax was incurred within 3 years of filing it would not be dischargeable. Check with your bankruptcy attorney about your tax issue and how it may relate to your filing.
This answer is general and is not intended to create an attorney client relationhsip and is for informational purposes only.