LLC and corporation are two different legal entities - no entity can be both at the same time.
Perhaps the point being made is that the default tax treatment for an LLC is pass-through, like an S corporation. You might find the post at the link below informative.
Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.
No. The IRS does recognize LLCs and allows you to elect corporate taxation if you wish. I suggest you find new accountants.
This response is for informational purposes only and is not offered as legal advice.
The above answers are correct and I believe that Dana has hit the nail on the head. The IRS does not recognize the LLC form, which is a creature of state statutory law.
The IRS considers your LLC as either a partnership or a corporation for purposes of your business' income tax. So, your accountants may be correct (though they are not explaining it clearly) in saying that you are a state LLC, but treated as a corporation by the IRS, if you have filed for S-Corp status.
Disclaimer: This response is made purely for educational reasons and I am not your attorney. You should refer all legal questions to your own counsel before making decisions.
You can be an LLC for state law and a C corporation for federal income tax purposes. The LLC is a state law entity; the entity's federal tax classification is a matter of federal tax law. If you form a state law LLC, you can check the box to be taxed as a corporation and then you would be taxed as a C corporation, but you would be an LLC for state law purposes.