IRS Letter 2645C is a notice that the IRS is delaying your case. It is extremely irritating. They often send several of these with delays successively. (See also Notice CP2006)
It is possible to push the IRS by using the Taxpayer Advocate, but that is time-consuming & they may refuse to review the case since normal procedures are being followed.
However, this type of delay might be a reason to escape the payment of interest, if you can show it was a ministerial act that delayed the case. But, don't argue that here - there is a separate procedure.
But, even so, the ultimate resolution depends upon the action of the IRS. When they are not acting, nothing gets done. You must follow up - don't depend on the IRS.
Tax attorney J. David Hopkins at TaxHelpLaw can get quick answers and action on your case! For more detailed information please follow the Prep Steps & contact Mr. Hopkins!