The IRS uses Letter 544C to inform you of some procedural adjustment of your account such as that you have full-paid the balance due for the tax year mentioned in the letter or that their previous letter was in error (example below).
But, if you owe for other tax years and you are making payments to the IRS do not stop making payments or you will default your agreement with the IRS and be required to go through the time-consuming procedure of disclosing your assets, liabilities and income to the IRS.
However, Letter 544C could be used to inform you of an error that requires your response.
Response to Letter 544C
If you agree with the IRS then there is no need to hire an attorney. But, if you have questions or problems, TaxHelpLaw can assist you.